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  1. Article: The contributions of plasma membrane Na+-Ca2+-exchange and the Ca2+-ATPase to the regulation of cytosolic calcium ([Ca2+]i) in a clonal pituitary cell line (AtT-20) of mouse corticotropes.

    Fiekers, J F

    Life sciences

    2001  Volume 70, Issue 6, Page(s) 681–698

    Abstract: Single cell calcium microfluorimetry was used to examine the regulation of [Ca2+]i homeostasis in a clonal cell line of corticotropes (AtT-20 cells). Single cells, loaded with fura-2/AM, were exposed briefly to elevated potassium chloride (KCI, 40 mM, 5 ... ...

    Abstract Single cell calcium microfluorimetry was used to examine the regulation of [Ca2+]i homeostasis in a clonal cell line of corticotropes (AtT-20 cells). Single cells, loaded with fura-2/AM, were exposed briefly to elevated potassium chloride (KCI, 40 mM, 5 sec). The time constant of decay of the [Ca2+]i signal was used as an index of [Ca2+]i extrusion and/or sequestration. Substitution of extracellular sodium with lithium, N-methyl-D-glucamine (NMDG), or Tris, increased resting levels of [Ca2+]i and significantly increased the time constant of [Ca2+]i decay by 40% compared to control indicating the participation of Na+-Ca2+-exchange. Prior exposure of single cells to thapsigargin (1 microM) or BuBHQ (10 microM). inhibitors of the SERCA Ca2+-ATPases, and/or the mitochondrial uncoupler FCCP (1 microM) did not significantly change the time constant of [Ca2+]i decay following KCl. Lanthanum ions (La3+), applied during the decay of the KCI-induced increase in [Ca2+]i, significantly increased the time constant of the return of [Ca2+]i to resting levels by 70% compared to control. Brief exposure of cells to sodium orthovanadate, an inhibitor of ATP-dependent pump activity, slowed and longer exposures prevented, the return of [Ca2+]i to resting levels. We conclude that neither intracellular SERCA pumps nor mitochondrial uptake contribute significantly to [Ca2+]i sequestration following a [Ca2+]i load and that the plasma membrane Ca2+-ATPase contributes to a greater extent than the Na+-Ca2+-exchanger to the return of [Ca2+]i to resting levels following a [Ca2+]i load under these experimental conditions.
    MeSH term(s) Animals ; Calcium-Transporting ATPases/antagonists & inhibitors ; Calcium-Transporting ATPases/metabolism ; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone/pharmacology ; Cell Line ; Cell Membrane/enzymology ; Clone Cells ; Enzyme Inhibitors/pharmacology ; Fura-2/pharmacology ; Hydroquinones/pharmacology ; Image Processing, Computer-Assisted ; Ionomycin/pharmacology ; Lithium/pharmacology ; Meglumine/pharmacology ; Meglumine Antimoniate ; Mice ; Organometallic Compounds/pharmacology ; Organophosphates/pharmacology ; Pituitary Gland/cytology ; Pituitary Gland/drug effects ; Pituitary Gland/enzymology ; Potassium Chloride/pharmacology ; Signal Transduction ; Sodium-Calcium Exchanger/antagonists & inhibitors ; Sodium-Calcium Exchanger/metabolism ; Tetraethylammonium/pharmacology ; Thapsigargin/pharmacology
    Chemical Substances Enzyme Inhibitors ; Hydroquinones ; Organometallic Compounds ; Organophosphates ; Sodium-Calcium Exchanger ; tris(2,3-dibromopropyl)phosphate (126-72-7) ; 2,5-di-tert-butylhydroquinone (26XK13B61B) ; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone (370-86-5) ; Ionomycin (56092-81-0) ; Tetraethylammonium (66-40-0) ; Potassium Chloride (660YQ98I10) ; Thapsigargin (67526-95-8) ; Meglumine (6HG8UB2MUY) ; Meglumine Antimoniate (75G4TW236W) ; Lithium (9FN79X2M3F) ; Calcium-Transporting ATPases (EC 3.6.3.8) ; Fura-2 (TSN3DL106G)
    Language English
    Publishing date 2001-12-28
    Publishing country Netherlands
    Document type Journal Article
    ZDB-ID 3378-9
    ISSN 1879-0631 ; 0024-3205
    ISSN (online) 1879-0631
    ISSN 0024-3205
    DOI 10.1016/s0024-3205(01)01443-6
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  2. Article: Sites and mechanisms of antibiotic-induced neuromuscular block: a pharmacological analysis using quantal content, voltage clamped end-plate currents and single channel analysis.

    Fiekers, J F

    Acta physiologica, pharmacologica et therapeutica latinoamericana : organo de la Asociacion Latinoamericana de Ciencias Fisiologicas y [de] la Asociacion Latinoamericana de Farmacologia

    1999  Volume 49, Issue 4, Page(s) 242–250

    Abstract: Since the original observation of Vital Brazil and Corrado (1957) concerning the antibiotic induced neuromuscular block produced by streptomycin, there has been considerable interest in the mechanisms responsible for not only neuromuscular block but also ...

    Abstract Since the original observation of Vital Brazil and Corrado (1957) concerning the antibiotic induced neuromuscular block produced by streptomycin, there has been considerable interest in the mechanisms responsible for not only neuromuscular block but also the effects of antibiotics on different systems. We used the voltage clamped end-plate of transacted skeletal muscle to examine the concentration-dependent actions of several groups of antibiotics. The aminoglycoside antibiotics, neomycin and streptomycin, were both more effective at reducing quantal release of acetylcholine (ACh) than interacting with the postjunctional ACh receptor-channel complex. Neomycin was approximately 10 X more potent prejunctionally than streptomycin and the prejunctional effects of each antibiotic were reversed competitively by raising extracellular calcium. Both neomycin and streptomycin also had postjunctional actions at higher concentrations. Neomycin interacted with the open state of the ACh receptor ion channel complex while streptomycin blocks the ACh receptor. The lincosamide antibiotics, lincomycin and clindamycin produced their neuromuscular block postjunctionally by interacting with the open state of the ACh-receptor channel complex. Clindamycin is approximately 20 X more effective at blocking the open channel than was lincomycin. Using cell attached patch clamp recordings in cultured rat myotubes, we demonstrated a lincosamide-induced block of open ion channels with clindamycin having a much slower unblocking rate than lincomycin. Using epimers of the lincosamides, we demonstrated that lipophilicity of the molecule, rather than stereochemical considerations, is important for open channel blockade affecting primarily the "off" rate of channel blocking. This mechanism appears important for not only the lincosamide antibiotics but also for the postjunctional actions of the aminoglycoside antibiotics, particularly neomycin.
    MeSH term(s) Animals ; Anti-Bacterial Agents/pharmacology ; Calcium/analysis ; Calcium Channels/drug effects ; Calcium Channels/metabolism ; Clindamycin/pharmacology ; Dose-Response Relationship, Drug ; Lincomycin/pharmacology ; Lincosamides ; Macrolides ; Muscle, Skeletal/drug effects ; Neomycin/pharmacology ; Neuromuscular Blockade ; Neuromuscular Blocking Agents/pharmacology ; Patch-Clamp Techniques ; Rats ; Receptors, Cholinergic/drug effects ; Receptors, Cholinergic/metabolism ; Streptomycin/pharmacology
    Chemical Substances Anti-Bacterial Agents ; Calcium Channels ; Lincosamides ; Macrolides ; Neuromuscular Blocking Agents ; Receptors, Cholinergic ; Neomycin (1404-04-2) ; Clindamycin (3U02EL437C) ; Lincomycin (BOD072YW0F) ; Calcium (SY7Q814VUP) ; Streptomycin (Y45QSO73OB)
    Language English
    Publishing date 1999
    Publishing country Argentina
    Document type Journal Article
    ZDB-ID 1096341-8
    ISSN 0327-6309
    ISSN 0327-6309
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  3. Article: Long-term potentiation of nicotinic synaptic transmission in rat superior cervical ganglia produced by phorbol ester and tetanic stimulation.

    Heppner, Thomas J / Fiekers, Jerome F

    Autonomic neuroscience : basic & clinical

    2003  Volume 105, Issue 1, Page(s) 35–44

    Abstract: The long-term potentiation of nicotinic synaptic transmission induced by both active phorbol ester (4beta-phorbol-12,13-dibutyrate, PdBu) and tetanic trains of preganglionic stimulation was studied in single neurons of the superior cervical ganglion (SCG) ...

    Abstract The long-term potentiation of nicotinic synaptic transmission induced by both active phorbol ester (4beta-phorbol-12,13-dibutyrate, PdBu) and tetanic trains of preganglionic stimulation was studied in single neurons of the superior cervical ganglion (SCG) of the rat using intracellular recording techniques. PdBu significantly increased the mean amplitude of both the unitary evoked fast excitatory postsynaptic potentials (EPSPs) and the fast excitatory postsynaptic currents (EPSCs) to 17.0+/-3.3 mV (control 8.4+/-1.9 mV, n=5) and 2.8+/-0.4 nA (control 0.8+/-0.1 nA, n=10), respectively. There was no significant change in either the resting membrane potential, input resistance, or the threshold for the initiation of an action potential. The response to exogenously applied acetylcholine (ACh) was also not changed following exposure to PdBu. In low-calcium, high-magnesium solutions, PdBu significantly increased the quantal content of EPSPs approximately threefold from a control of 0.9+/-0.2 (n=5) to 2.6+/-0.6 (n=5). The quantal content of EPSCs was also increased to 1.3+/-0.2 (control 0.5+/-0.1, n=10). PdBu increased the frequency of miniature EPSPs (mEPSPs) to 196+/-47% (n=6) of control, while the amplitude, rise time, rate of rise, and decay of mEPSPs were not significantly changed. Tetanic stimulation significantly increased the amplitude of the unitary synaptic EPSPs and EPSCs without significantly changing the resting membrane potential, input resistance, threshold for initiation of an action potential, or the response to exogenously applied ACh. Tetanic stimulation significantly increased quantal content of EPSPs and EPSCs threefold. The results obtained with tetanically induced LTP are similar to the results obtained with phorbol ester-induced LTP in these ganglion neurons. These results suggest that both tetanically induced and phorbol ester-induced LTP, in the rat, share similar mechanisms which involve, at least in part, activation of PKC-dependent mechanisms to increase quantal release from sympathetic preganglionic axon terminals.
    MeSH term(s) Animals ; Electric Stimulation/methods ; Excitatory Postsynaptic Potentials/drug effects ; Excitatory Postsynaptic Potentials/physiology ; In Vitro Techniques ; Long-Term Potentiation/drug effects ; Long-Term Potentiation/physiology ; Phorbol Esters/pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Nicotinic/physiology ; Superior Cervical Ganglion/drug effects ; Superior Cervical Ganglion/physiology ; Synaptic Transmission/drug effects ; Synaptic Transmission/physiology
    Chemical Substances Phorbol Esters ; Receptors, Nicotinic
    Language English
    Publishing date 2003-04-30
    Publishing country Netherlands
    Document type Journal Article ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 2020105-9
    ISSN 1872-7484 ; 1566-0702
    ISSN (online) 1872-7484
    ISSN 1566-0702
    DOI 10.1016/S1566-0702(03)00024-9
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  4. Article: Concentration-dependent effects of neostigmine on the endplate acetylcholine receptor channel complex.

    Fiekers, J F

    The Journal of neuroscience : the official journal of the Society for Neuroscience

    1985  Volume 5, Issue 2, Page(s) 502–514

    Abstract: The concentration-dependent actions of neostigmine, a carbamate anticholinesterase agent, were studied on the acetylcholine receptor channel complex in voltage-clamped twitch fibers of costocutaneous muscles of garter snakes. Low concentrations of ... ...

    Abstract The concentration-dependent actions of neostigmine, a carbamate anticholinesterase agent, were studied on the acetylcholine receptor channel complex in voltage-clamped twitch fibers of costocutaneous muscles of garter snakes. Low concentrations of neostigmine (10(-6) or 10(-5) M) increased miniature endplate current (MEPC) amplitude and the time constant of MEPC decay without changing the relationship between the MEPC decay time constant and membrane potential. Acetylcholine- or carbachol-induced endplate current fluctuation spectra were well fitted by a single Lorentzian curve with a characteristic frequency and single-channel conductance unaltered by low concentrations of neostigmine. Concentrations of neostigmine greater than 5 X 10(-5) M decreased MEPC amplitude and split the decay of MEPCs into two components, one faster and one slower than the control rate. These effects were both voltage and concentration dependent. Spectra of current fluctuations recorded in concentrations greater than or equal to 5 X 10(-5) M neostigmine required two time constants, one faster and one slower than the control. Two component spectra were also obtained with carbachol-induced current fluctuation spectra, indicating that these effects of neostigmine were direct and not a consequence of acetylcholinesterase inhibition. Similar results were also obtained in muscles pretreated with collagenase to remove junctional acetylcholinesterase. The fast and slow time constants obtained from current fluctuation spectra decreased and increased, respectively, with either increases in the concentration of neostigmine or membrane hyperpolarization when analyzed in the same fiber. The effects of neostigmine on channel lifetime were reversible with washing. These results indicate that the effects of neostigmine are concentration dependent. Concentrations greater than 2.5 X 10(-5) M exhibit direct effects on the endplate receptor channel complex which are unrelated to acetylcholinesterase inhibition. These actions include: a prolongation of the gating kinetics of the endplate receptor channel complex, the production of an altered state of the receptor channel complex evidenced by a high frequency component to current fluctuation spectra, and a direct action to block the acetylcholine receptor.
    MeSH term(s) Animals ; Carbachol/pharmacology ; Ion Channels/drug effects ; Membrane Potentials/drug effects ; Microbial Collagenase/pharmacology ; Motor Endplate/metabolism ; Neostigmine/pharmacology ; Neuromuscular Junction/metabolism ; Osmolar Concentration ; Receptors, Cholinergic/drug effects ; Snakes
    Chemical Substances Ion Channels ; Receptors, Cholinergic ; Neostigmine (3982TWQ96G) ; Carbachol (8Y164V895Y) ; Microbial Collagenase (EC 3.4.24.3)
    Language English
    Publishing date 1985-02
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 604637-x
    ISSN 1529-2401 ; 0270-6474
    ISSN (online) 1529-2401
    ISSN 0270-6474
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  5. Article: Interactions of edrophonium, physostigmine and methanesulfonyl fluoride with the snake end-plate acetylcholine receptor-channel complex.

    Fiekers, J F

    The Journal of pharmacology and experimental therapeutics

    1985  Volume 234, Issue 3, Page(s) 539–549

    Abstract: The actions of two reversible anticholinesterase agents, edrophonium and physostigmine, were compared with the irreversible agent methanesulfonyl fluoride (MSF) on miniature end-plate currents (MEPCs) and ACh-induced end-plate current fluctuations ... ...

    Abstract The actions of two reversible anticholinesterase agents, edrophonium and physostigmine, were compared with the irreversible agent methanesulfonyl fluoride (MSF) on miniature end-plate currents (MEPCs) and ACh-induced end-plate current fluctuations recorded from twitch fibers of costocutaneous muscles of garter snakes (Thamnophis sp.). Low concentrations of edrophonium (less than 25 microM) produced a concentration-dependent increase in both the MEPC amplitude and the time constant of MEPC decay. MEPCs recorded at all concentrations studied (25-100 microM) decayed as a single exponential function with time. As the concentration of edrophonium was increased, MEPC amplitude was initially increased and then decreased such that, at concentrations above 50 microM, MEPC amplitude was decreased below control values. Concentrations of edrophonium greater than 30 microM produced power density spectra that required the sum of two Lorentzian components--one faster and one slower than control. Single-channel conductance was not significantly altered by edrophonium. Low concentrations of physostigmine (less than 10 microM) increased MEPC amplitude and prolonged MEPC decay. Higher concentrations of physostigmine (10-100 microM) decreased mean peak MEPC amplitude and accelerated MEPC decay in a concentration-dependent manner. The relationship between MEPC decay and membrane potential was reduced, and then reversed, with increasing concentrations of physostigmine. Current fluctuation spectra recorded in physostigmine were described by a single Lorentzian function at all membrane voltages and concentrations studied. Increasing the concentration of physostigmine or membrane hyperpolarization did not alter single-channel conductance but shortened the apparent lifetime of open end-plate channels. MSF increased MEPC amplitude and increased the time constant of MEPC decay without altering the temperature and voltage dependence of both MEPC decay and channel lifetime determined from end-plate current fluctuations. Exposure of MSF-treated end-plates to either edrophonium or physostigmine produced results that were similar to those obtained before MSF treatment. These results demonstrate that edrophonium and physostigmine have direct actions on the end-plate receptor-channel complex that are unrelated to their inhibitory action on junctional acetylcholinesterase.
    MeSH term(s) Acetylcholine/pharmacology ; Animals ; Cholinesterase Inhibitors/pharmacology ; Edrophonium/pharmacology ; In Vitro Techniques ; Ion Channels/drug effects ; Membrane Potentials/drug effects ; Motor Endplate/drug effects ; Motor Endplate/physiology ; Neostigmine/pharmacology ; Neuromuscular Junction/drug effects ; Physostigmine/pharmacology ; Receptors, Cholinergic/drug effects ; Snakes ; Sulfones/pharmacology
    Chemical Substances Cholinesterase Inhibitors ; Ion Channels ; Receptors, Cholinergic ; Sulfones ; Neostigmine (3982TWQ96G) ; Edrophonium (70FP3JLY7N) ; methanesulfonyl fluoride (9H250YYY0R) ; Physostigmine (9U1VM840SP) ; Acetylcholine (N9YNS0M02X)
    Language English
    Publishing date 1985-09
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 3106-9
    ISSN 1521-0103 ; 0022-3565
    ISSN (online) 1521-0103
    ISSN 0022-3565
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  6. Article: Effects of the aminoglycoside antibiotics, streptomycin and neomycin, on neuromuscular transmission. I. Presynaptic considerations.

    Fiekers, J F

    The Journal of pharmacology and experimental therapeutics

    1983  Volume 225, Issue 3, Page(s) 487–495

    Abstract: The effects of two aminoglycoside antibiotics, streptomycin and neomycin, were studied in voltage-clamped transected twitch fibers of the costocutaneous muscles of garter snakes (species Thamnophis). The concentration-dependent effects of each antibiotic ...

    Abstract The effects of two aminoglycoside antibiotics, streptomycin and neomycin, were studied in voltage-clamped transected twitch fibers of the costocutaneous muscles of garter snakes (species Thamnophis). The concentration-dependent effects of each antibiotic were quantitated by measuring miniature end-plate currents (mepcs) and evoked end-plate currents (epcs) in a single fiber before and in the presence of a wide range of concentrations of each antibiotic. The amplitude and the kinetics of these currents were studied and estimates of the quantal content of evoked transmitter release determined by the direct method of mean ratios, epc/mepc. A distinct separation was obtained between the concentrations of each antibiotic which demonstrated either pre- or postsynaptic actions. Both streptomycin and neomycin produced a concentration-dependent reduction in epc amplitude at concentrations which did not reduce mepc amplitude. Thus, the primary site of action for these antibiotics was considered of presynaptic origin. Streptomycin was approximately one-tenth as active as neomycin in reducing quantal release of acetylcholine. The marked depression in epc amplitude and quantal content produced by high concentrations of each antibiotic were reversed by elevating the external calcium concentration. Double logarithmic plots of the relationship between external calcium concentration and epc amplitude yielded a slope of approximately 3.8 in control physiological solution. In the presence of blocking concentrations of each antibiotic, increasing the external calcium concentration caused a parallel shift to the right of this relationship. These results suggest that the major mechanism for the neuromuscular depression produced by these aminoglycoside antibiotics is a competitive antagonism with calcium for a common presynaptic site required for evoked transmitter release.
    MeSH term(s) Animals ; Evoked Potentials/drug effects ; Membrane Potentials/drug effects ; Neomycin/pharmacology ; Neuromuscular Junction/drug effects ; Neuromuscular Junction/physiology ; Snakes ; Streptomycin/pharmacology ; Synapses/drug effects ; Synapses/physiology ; Synaptic Transmission/drug effects
    Chemical Substances Neomycin (1404-04-2) ; Streptomycin (Y45QSO73OB)
    Language English
    Publishing date 1983-06
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 3106-9
    ISSN 1521-0103 ; 0022-3565
    ISSN (online) 1521-0103
    ISSN 0022-3565
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  7. Article: Effects of the aminoglycoside antibiotics, streptomycin and neomycin, on neuromuscular transmission. II. Postsynaptic considerations.

    Fiekers, J F

    The Journal of pharmacology and experimental therapeutics

    1983  Volume 225, Issue 3, Page(s) 496–502

    Abstract: The postsynaptic effects of two aminoglycoside antibiotics, streptomycin and neomycin, were studied on miniature end-plate currents (mepcs) and acetylcholine-induced end-plate current fluctuations in voltage-clamped costocutaneous muscles of the garter ... ...

    Abstract The postsynaptic effects of two aminoglycoside antibiotics, streptomycin and neomycin, were studied on miniature end-plate currents (mepcs) and acetylcholine-induced end-plate current fluctuations in voltage-clamped costocutaneous muscles of the garter snake (species Thamnophis). Neomycin decreased the amplitude of mepcs and accelerated the time constants of mepc decay in a concentration-dependent manner without altering the single exponential nature of mepc decay. Neomycin also produced a voltage- and concentration-dependent nonlinearity in the current/voltage relationship. The relationship between the time constants of mepc decay and membrane potential was progressively reduced with increasing concentrations of neomycin. A concentration-dependent reduction in single channel conductance and channel lifetime was also obtained with neomycin. In contrast, streptomycin, in concentrations up to 5 X 10(-5) M, did not significantly alter either mepc amplitude, the time constant of mepc decay, the relationship between the mepc decay time constant and membrane potential or the lifetime and conductance of single end-plate channels. In very high concentrations (greater than 1 mM) streptomycin decreased mepc amplitude and prolonged mepc decay at hyperpolarized membrane potentials. The results suggest that neomycin interacts with the ionic channels of the acetylcholine receptor in their open configuration, whereas streptomycin acts primarily by blocking the receptor. The significant differences in the molecular actions of these two antibiotics may provide an explanation for the observed differences in the character and reversal of the neuromuscular block produced by these antibiotics.
    MeSH term(s) Animals ; Electric Conductivity ; Evoked Potentials/drug effects ; Membrane Potentials/drug effects ; Motor Endplate/drug effects ; Motor Endplate/physiology ; Neomycin/pharmacology ; Neuromuscular Junction/drug effects ; Neuromuscular Junction/physiology ; Snakes ; Streptomycin/pharmacology ; Synapses/drug effects ; Synapses/physiology ; Synaptic Transmission/drug effects
    Chemical Substances Neomycin (1404-04-2) ; Streptomycin (Y45QSO73OB)
    Language English
    Publishing date 1983-06
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 3106-9
    ISSN 1521-0103 ; 0022-3565
    ISSN (online) 1521-0103
    ISSN 0022-3565
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  8. Article: Spontaneous transients of [Ca2+]i depend on external calcium and the activation of L-type voltage-gated calcium channels in a clonal pituitary cell line (AtT-20) of cultured mouse corticotropes.

    Fiekers, J F / Konopka, L M

    Cell calcium

    1996  Volume 19, Issue 4, Page(s) 327–336

    Abstract: Spontaneous transients of [Ca2+]i were recorded from single nonstimulated cells of a clonal pituitary cell line of corticotropes, AtT-20/D16v. The spontaneous [Ca2+]i transients were dependent on calcium entry from the extracellular solution because they ...

    Abstract Spontaneous transients of [Ca2+]i were recorded from single nonstimulated cells of a clonal pituitary cell line of corticotropes, AtT-20/D16v. The spontaneous [Ca2+]i transients were dependent on calcium entry from the extracellular solution because they were abolished both in the absence of extracellular calcium and with the addition of cobalt to the calcium-containing extracellular solution. Calcium entry occurred through voltage-gated (VGCC) L-type calcium channels because the [Ca2+]i transients were blocked by L-type calcium channel antagonists, e.g. nifedipine, and were unaffected by the addition of tetrodotoxin. Bay K 8644 (1 microM) induced transient increases in [Ca2+]i which were also blocked reversibly by either the absence of extracellular calcium or the addition of an L-type calcium channel antagonist (e.g. nifedipine). The resting levels of [Ca2+]i and the frequency, but not the amplitude or duration, of the spontaneous [Ca2+]i transients increased as the concentration of extracellular calcium was elevated in concentrations ranging from 1.8-7.2 mM. Potassium depolarization reversibly elevated resting levels of [Ca2+]i and initiated the spontaneous calcium transients. These results indicate that extracellular calcium modulates the frequency of spontaneous [Ca2+]i transients in AtT-20 cells which are caused by the activation of L-type calcium channels by a spontaneous increase in the permeability of the cell membrane to calcium.
    MeSH term(s) Animals ; Calcium ; Calcium Channels/physiology ; Cell Line ; Cells, Cultured ; Clone Cells ; Ion Channel Gating ; Mice ; Pituitary Gland, Anterior/cytology
    Chemical Substances Calcium Channels ; Calcium (SY7Q814VUP)
    Language English
    Publishing date 1996-04
    Publishing country Netherlands
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 757687-0
    ISSN 1532-1991 ; 0143-4160
    ISSN (online) 1532-1991
    ISSN 0143-4160
    DOI 10.1016/s0143-4160(96)90073-1
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  9. Article: Neuromuscular block produced by polymyxin B: interaction with end-plate channels.

    Fiekers, J F

    European journal of pharmacology

    1981  Volume 70, Issue 1, Page(s) 77–81

    Abstract: The effect of polymyxin B on the amplitude and kinetics of miniature end-plate currents and acetylcholine-induced current fluctuations was studied in voltage-clamped fibers of the snake. Polymyxin B produced a voltage and concentration dependent ... ...

    Abstract The effect of polymyxin B on the amplitude and kinetics of miniature end-plate currents and acetylcholine-induced current fluctuations was studied in voltage-clamped fibers of the snake. Polymyxin B produced a voltage and concentration dependent reduction in both mean peak MEPC amplitude and the time constant of MEPC decay. A concomitant decrease in mean channel lifetime and single channel conductance indicated that a major mechanism for the neuromuscular block produced by polymyxin B is endplate channel blockade.
    MeSH term(s) Animals ; In Vitro Techniques ; Ion Channels/drug effects ; Membrane Potentials/drug effects ; Motor Endplate/drug effects ; Neuromuscular Blocking Agents ; Neuromuscular Junction/drug effects ; Polymyxin B/pharmacology ; Polymyxins/pharmacology ; Snakes
    Chemical Substances Ion Channels ; Neuromuscular Blocking Agents ; Polymyxins ; Polymyxin B (J2VZ07J96K)
    Language English
    Publishing date 1981-03-05
    Publishing country Netherlands
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Research Support, U.S. Gov't, P.H.S.
    ZDB-ID 80121-5
    ISSN 1879-0712 ; 0014-2999
    ISSN (online) 1879-0712
    ISSN 0014-2999
    DOI 10.1016/0014-2999(81)90435-0
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Article: Calcium homeostasis in a clonal pituitary cell line of mouse corticotropes.

    Fiekers, J F / Gelbspan, D / Heppner, T J

    Canadian journal of physiology and pharmacology

    2001  Volume 79, Issue 6, Page(s) 502–511

    Abstract: Calcium homeostasis was studied following a depolarization-induced transient increase in [Ca2+]i in single cells of the clonal pituitary cell line of corticotropes, AtT-20 cells. The KCl-induced increase in [Ca2+]i was blocked in (i) extracellular ... ...

    Abstract Calcium homeostasis was studied following a depolarization-induced transient increase in [Ca2+]i in single cells of the clonal pituitary cell line of corticotropes, AtT-20 cells. The KCl-induced increase in [Ca2+]i was blocked in (i) extracellular calcium-deficient solutions, (ii) external cobalt (2.0 mM), (iii) cadmium (200 microM), and (iv) nifedipine (2.0 microM). The mean increase in [Ca2+]i in single cells in the presence of an uncoupler of mitochondrial function [carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone, FCCP, 1 microM] was 54 +/- 13 nM (n = 9). The increase in [Ca2+]i produced by FCCP was greater either during or following a KCl-induced [Ca2+]i load. However, FCCP did not significantly alter the clearance of calcium during a KCl-induced rise in [Ca2+]i. Fifty percent of the cells responded to caffeine (10 mM) with an increase in [Ca2+]i (191 +/- 24 nM; n = 21) above resting levels; this effect was blocked by ryanodine (10 microM). Thapsigargin (2 microM) and 2,5 di(-t-butyl)-1,4 hydroquinone (BuBHQ, 10 microM) produced increases in [Ca2+]i (47 +/- 11 nM, n = 6 and 22 +/- 4 nM, n = 8, respectively) that increased cell excitability. These results support a role for mitochondria and sarco-endoplasmic reticulum calcium stores in cytosolic [Ca2+]i regulation; however, none of these organelles are primarily responsible for the return of [Ca2+]i to resting levels following this KCl-induced [Ca2+]i load.
    MeSH term(s) Adrenocorticotropic Hormone/biosynthesis ; Animals ; Antimetabolites/pharmacology ; Caffeine/pharmacology ; Calcium/metabolism ; Calcium-Transporting ATPases/metabolism ; Clone Cells ; Cytosol/drug effects ; Cytosol/metabolism ; Homeostasis/drug effects ; Homeostasis/physiology ; Inositol 1,4,5-Trisphosphate/metabolism ; Mice ; Mitochondria/drug effects ; Mitochondria/metabolism ; Organoids/drug effects ; Organoids/metabolism ; Phosphodiesterase Inhibitors/pharmacology ; Pituitary Gland/cytology ; Pituitary Gland/drug effects ; Pituitary Gland/metabolism ; Potassium/metabolism ; Potassium Chloride/pharmacology ; Sarcoplasmic Reticulum Calcium-Transporting ATPases
    Chemical Substances Antimetabolites ; Phosphodiesterase Inhibitors ; Caffeine (3G6A5W338E) ; Potassium Chloride (660YQ98I10) ; Inositol 1,4,5-Trisphosphate (85166-31-0) ; Adrenocorticotropic Hormone (9002-60-2) ; Calcium-Transporting ATPases (EC 3.6.3.8) ; Sarcoplasmic Reticulum Calcium-Transporting ATPases (EC 3.6.3.8) ; Potassium (RWP5GA015D) ; Calcium (SY7Q814VUP)
    Language English
    Publishing date 2001-06
    Publishing country Canada
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 127527-6
    ISSN 1205-7541 ; 0008-4212
    ISSN (online) 1205-7541
    ISSN 0008-4212
    Database MEDical Literature Analysis and Retrieval System OnLINE

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