P-type Ca2+ current in crayfish peptidergic neurones

1999 ◽  
Vol 202 (4) ◽  
pp. 429-440 ◽  
Author(s):  
J. García-Colunga ◽  
R. Valdiosera ◽  
U. García
Keyword(s):  
Time Course ◽  
Divalent Cations ◽  
Constant Field ◽  
Voltage Range ◽  
Current Voltage ◽  
Boltzmann Function ◽  
P Type ◽  
Current Voltage Relationship ◽  
Voltage Relationship ◽  
Ca2 Channels

Inward Ca2+ current through voltage-gated Ca2+ channels was recorded from freshly dissociated crayfish X-organ (XO) neurones using the whole-cell voltage-clamp technique. Changing the holding potential from −50 to −90 mV had little effect on the characteristics of the current-voltage relationship: neither the time course nor the amplitude of the Ca2+ current was affected. Inactivation of the Ca2+ current was observed over a small voltage range, between −35 and −10 mV, with half-inactivation at −20 mV. The activation of the Ca2+ current was modelled using Hodgkin-Huxley kinetics. The time constant of activation, τ m, was 568+/−66 micros at −20 mV and decreased gradually to 171+/−23 micros at 40 mV (means +/− s.e.m., N=5). The steady-state activation, m(infinity), was fitted with a Boltzmann function, with a half-activation voltage of −7.45 mV and an apparent threshold at −40 mV. The instantaneous current-voltage relationship was adjusted using the Goldman-Hodgkin-Katz constant-field equation, giving a permeation of 4.95×10(−5)cm s-1. The inactivation of the Ca2+ current in XO neurones was dependent on previous entry of Ca2+. Using a double-pulse protocol, the inactivation was fitted to a U-shaped curve with a maximal inactivation of 35 % at 30 mV. The time course of the recovery from inactivation was fitted with an exponential function. The time constants were 17+/−2.6 ms for a prepulse of 10 ms and 31+/−3.2 ms for a prepulse of 20 ms. The permeability sequence of the Ca2+ channels was as follows: Ba2+>Sr2+~Ca2+>>Mg2+. Other divalent cations blocked the Ca2+ current, and their effects were voltage-dependent; the potency of blockage was Cd2+~Zn2+>>Co2+~Ni2+. The peptide ω -agatoxin-IVA, a selective toxin for P-type Ca2+ channels, blocked 85 % of the Ca2+ current in XO neurones at 200 nmol l-1, but the current was insensitive to dihydropyridines, phenylalkylamines, ω -conotoxin-GVIA and ω -conotoxin-MVIIC, which are blockers of L-, N- and Q-type Ca2+ channels, respectively. From the voltage- and Ca2+-dependent kinetics, the higher permeability to Ba2+ than to Ca2+ and the higher sensitivity of the current to Cd2+ than to Ni2+, we conclude that the Ca2+ current in XO neurones is generated by high-voltage-activated (HVA) channels. Furthermore, its blockage by ω -agatoxin-IVA suggests that it is mainly generated through P-type Ca2+ channels.

scholarly journals Acetylcholine-induced current in perfused rat myoballs.

1980 ◽  
Vol 75 (3) ◽  
pp. 297-321 ◽  
Author(s):  
R Horn ◽  
M S Brodwick
Keyword(s):  
Membrane Potential ◽  
Time Course ◽  
Striated Muscle ◽  
Membrane Surface ◽  
Reversal Potential ◽  
Neonatal Rat ◽  
Resting Potential ◽  
Current Voltage ◽  
Current Voltage Relationship ◽  
Voltage Relationship

Spherical "myoballs" were grown under tissue culture conditions from striated muscle of neonatal rat thighs. The myoballs were examined electrophysiologically with a suction pipette which was used to pass current and perfuse internally. A microelectrode was used to record membrane potential. Experiments were performed with approximately symmetrical (intracellular and extracellular) sodium aspartate solutions. The resting potential, acetylcholine (ACh) reversal potential, and sodium channel reversal potential were all approximately 0 mV. ACh-induced currents were examined by use of both voltage jumps and voltage ramps in the presence of iontophoretically applied agonist. The voltage-jump relaxations had a single exponential time-course. The time constant, tau, was exponentially related to membrane potential, increasing e-fold for 81 mV hyperpolarization. The equilibrium current-voltage relationship was also approximately exponential, from -120 to +81 mV, increasing e-fold for 104 mV hyperpolarization. The data are consistent with a first-order gating process in which the channel opening rate constant is slightly voltage dependent. The instantaneous current-voltage relationship was sublinear in the hyperpolarizing direction. Several models are discussed which can account for the nonlinearity. Evidence is presented that the "selectivity filter" for the ACh channel is located near the intracellular membrane surface.

Gap junction channel gating at bass retinal electrical synapses

1996 ◽  
Vol 13 (6) ◽  
pp. 1049-1057 ◽  
Author(s):  
Chengbiao Lu ◽  
Douglas G. McMahon
Keyword(s):  
Time Constant ◽  
Time Course ◽  
Single Channel ◽  
Horizontal Cells ◽  
Electrical Synapses ◽  
Dependent Inactivation ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Current Voltage Relationship ◽  
Voltage Relationship

AbstractTo further characterize the properties of retinal horizontal cell electrical synapses, we have studied the gating characteristics of gap junctions between cone-driven horizontal cells from the hybrid striped bass retina using double whole-cell voltage-clamp techniques. In a total of 105 cell pairs, the macroscopic conductance ranged from 0.4–100 nS with most cell pairs exhibiting junctional conductances between 10 and 30 nS. The junctional current-voltage relationship showed that peak or instantaneous currents (Iinst) were linear within the Vj range of ±100 mV and that steady-state junctional currents (Iss) exhibited rectification with increasing voltage beginning around ±30–40 mV Vj. The normalized junctional current-voltage relationship was well fit by a two-state Boltzmann distribution, with an effective gating charge of 1.9 charges/channel, a half-maximal voltage of approximately ±55 mV, and a normalized residual conductance of 0.28. The decay of junctional current followed a single exponential time course with the time constant decreasing with increasing Vj. Recovery of junctional current from voltage-dependent inactivation takes about 1 s following a pulse of 80 mV, and is about five times slower than the inactivation time course at the same Vj. Single-channel analysis showed that the unitary conductance of junctional channels is 50–70 pS. The overall open probability decreased in a voltage-dependent manner. Both the mean channel open time and the frequency of channel opening decreased, while the channel closure time increased. The ratio of closed time/total recording time significantly increased as Vj increased. Increased Vj reduced the number of events at all levels and shifted the unitary conductance to a lower level. Kinetic analysis of channel open duration showed that the distribution of channel open times was best fit by two exponentials and increased Vj significantly reduced the slower time constant. These results indicate that bass retina horizontal cells exhibit voltage-dependent inactivation of macroscopic junctional current. The inactivation occurs at the single-channel level mainly by increasing the rate of closure of voltage-sensitive channels.

scholarly journals Voltage- and time-dependent action of histrionicotoxin on the endplate current of the frog muscle.

1978 ◽  
Vol 72 (3) ◽  
pp. 351-367 ◽  
Author(s):  
L M Masukawa ◽  
E X Albuquerque
Keyword(s):  
Time Course ◽  
Ionic Channel ◽  
Time Dependent ◽  
Peak Amplitude ◽  
Endplate Current ◽  
Current Voltage ◽  
Initial Activation ◽  
Relationship Of ◽  
Current Voltage Relationship ◽  
Voltage Relationship

Histrionicotoxin, a toxin isolated from skin secretions of a Colombian arrow poison frog, Dendrobates histrionicus, decreased the amplitude and time-course of the endplate current, and altered the voltage dependence of the half-decay time. In addition, the toxin produced a characteristic nonlinearity in the current-voltage relationship of the endplate current when 3-s voltage conditioning steps were used. Reduction in time of the conditioning steps to 10 ms made the current-voltage relationship linear. The decrease in peak amplitude of the endplate current (epc) produced by histrionicotoxin measured during long hyperpolarizing conditioning steps was fitted by a single exponential function. The calculated rate constants ranged from 0.03 to 0.14 s-1 and varied with membrane potential at hyperpolarizing levels. The voltage- and time-dependent action of histrionicotoxin does not require an initial activation of receptors by acetylcholine (ACh). The characteristic of the current-voltage relationship can be accounted for by the observed voltage and time dependency of the attenuation of the endplate current amplitude in the presence of histrionicotoxin during long conditioning steps. These effects of histrionicotoxin on the peak amplitude, and on the voltage and time dependence of the epc were concentration-dependent and slowly reversible upon washing out the toxin. Thus, the voltage- and time-dependent action of histrionicotoxin at the endplate is related to an increase in the affinity between the toxin and the ACh receptor-ionic channel complex. This increase in affinity is postulated to be due to a conformational change of the macromolecule in the presence of histrionicotoxin which is demonstrated to be relatively slow, i.e., on the order of tens of seconds.

More than One Type of Conductance is Activated During Responses of Blowfly Monopolar Neurones

1989 ◽  
Vol 144 (1) ◽  
pp. 147-154 ◽  
Author(s):  
M. WECKSTRÖM ◽  
E. KOUVALAINEN ◽  
K. DJUPSUND ◽  
M. JÄRVILEHTO
Keyword(s):  
Compound Eye ◽  
Reversal Potential ◽  
Input Resistance ◽  
Current Clamp ◽  
Voltage Range ◽  
Continuous Release ◽  
Linear Current ◽  
Current Voltage ◽  
Current Voltage Relationship ◽  
Voltage Relationship

The principal second-order neurones in the blowfly compound eye, the large monopolar neurones (LMCs), were studied using intracellular recording and discontinuous current-clamp techniques, in combination with measurement of dynamic input resistance. The LMCs had resting potentials of −35 to −45 mV and showed a linear current-voltage relationship in the lamina in the physiological voltage range. The hyperpolarizing light-on transient was associated with a drop in input resistance from 17 ± 5 to 3 ± 1MΩ, and had a reversal potential between −60 and −90 mV. The dynamic input resistance of saturated responses and the properties of reversed responses suggested that more than one conductance was activated during the response of the LMCs. In lamina recordings, the input resistance increased beyond the resting level during repolarization, which can be interpreted in terms of a continuous release of transmitter by the photoreceptor terminals, even in darkness. The input resistance of LMCs in axon recordings in darkness and during the light-on response was generally higher than in the lamina recordings. The responses to light in axons also differed from those recorded in lamina by showing regenerative properties.

Human fetal central neurons in culture: voltage- and ligand-gated currents

1995 ◽  
Vol 74 (5) ◽  
pp. 1889-1899 ◽  
Author(s):  
D. W. Sah
Keyword(s):  
Current Density ◽  
Potassium Current ◽  
Time Course ◽  
Voltage Dependence ◽  
Sodium Current ◽  
Sodium Currents ◽  
Current Voltage ◽  
Channel Currents ◽  
Current Voltage Relationship ◽  
Voltage Relationship

1. The functional properties of sodium, potassium, calcium, N-methyl-D-aspartate (NMDA), kainate, and gamma-aminobutyric acid (GABA) currents were studied in dissociated monolayer cultures of fetal human brain neurons, using the whole cell patch-clamp technique. 2. Sodium currents were characterized with respect to the following properties: current density, voltage dependence of activation, voltage dependence of inactivation, and sensitivity to tetrodotoxin (TTX). All sodium currents exhibited voltage dependencies of activation and inactivation, and sensitivities to TTX that are characteristic of the neuronal form of the sodium current. 3. At least two types of potassium current were present, resembling the delayed rectifier and fast-inactivating potassium current. These two types of potassium current were distinguishable by their different kinetics, voltage dependencies of activation and inactivation, and sensitivities to 4-aminopyridine and tetraethylammonium. 4. High-voltage-activated calcium channel currents were present and were characterized with respect to current density, voltage dependencies of activation and inactivation, and sensitivity to cadmium. Low-voltage-activated calcium channel currents were also present. 5. NMDA- and kainate-gated currents were studied with respect to current density, time course, and current-voltage relationship. Kainate currents were also characterized with respect to inhibition by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). In addition, NMDA and kainate responses were compared for cortical versus cerebellar neurons. NMDA responses, which are only found in neurons, were present, confirming the neuronal phenotype suggested by the presence of the neuronal form of the sodium current. Nondesensitizing kainate currents were also present, with a half-maximally effective concentration (EC50) of approximately 200 microM for kainate; CNQX inhibited the kainate current with a half-inactivating concentration of 0.55 microM. 6. GABA-gated currents were characterized with respect to current density, time course, receptor subtype, desensitization, dose response, current-voltage relationship, ionic selectivity, pharmacology, and potentiation by the neurosteroid 5 alpha-pregnan-3 alpha-ol-11,20-dione (alfaxalone). Desensitizing GABAA currents were selective for chloride, inhibited by bicuculline and tert-butyl-bicyclophosphorothionate, and potentiated by diazepam, pentobarbital sodium, and alfaxalone. The EC50 for GABA was 15 microM.

scholarly journals Plasticity of calcium-permeable AMPA glutamate receptors in Pro-opiomelanocortin neurons

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Shigetomo Suyama ◽  
Alexandra Ralevski ◽  
Zhong-Wu Liu ◽  
Marcelo O Dietrich ◽  
Toshihiko Yada ◽  
...  
Keyword(s):  
Food Deprivation ◽  
High Fat Diet ◽  
Receptor Complex ◽  
High Fat ◽  
Fasted State ◽  
Linear Current ◽  
Current Voltage ◽  
Relationship Of ◽  
Current Voltage Relationship ◽  
Voltage Relationship

POMC neurons integrate metabolic signals from the periphery. Here, we show in mice that food deprivation induces a linear current-voltage relationship of AMPAR-mediated excitatory postsynaptic currents (EPSCs) in POMC neurons. Inhibition of EPSCs by IEM-1460, an antagonist of calcium-permeable (Cp) AMPARs, diminished EPSC amplitude in the fed but not in the fasted state, suggesting entry of GluR2 subunits into the AMPA receptor complex during food deprivation. Accordingly, removal of extracellular calcium from ACSF decreased the amplitude of mEPSCs in the fed but not the fasted state. Ten days of high-fat diet exposure, which was accompanied by elevated leptin levels and increased POMC neuronal activity, resulted in increased expression of Cp-AMPARs on POMC neurons. Altogether, our results show that entry of calcium via Cp-AMPARs is inherent to activation of POMC neurons, which may underlie a vulnerability of these neurons to calcium overload while activated in a sustained manner during over-nutrition.

Capsaicin and nicotine both activate a subset of rat trigeminal ganglion neurons

1996 ◽  
Vol 270 (6) ◽  
pp. C1807-C1814 ◽  
Author(s):  
L. Liu ◽  
S. A. Simon
Keyword(s):  
Trigeminal Ganglion ◽  
Acetylcholine Receptors ◽  
Ganglion Cells ◽  
Whole Cell Patch Clamp ◽  
Current Voltage ◽  
Trigeminal Ganglion Neurons ◽  
Ganglion Neurons ◽  
Relationship Of ◽  
Current Voltage Relationship ◽  
Voltage Relationship

Nicotine and capsaicin produce many similar physiological responses that include pain, irritation, and vasodilation. To determine whether neuronal nicotine acetylcholine receptors (nAChR) are present on capsaicin-sensitive neurons, whole cell patch-clamp recordings were performed on rat trigeminal ganglion cells. It was found that approximately 20% of the total number of neurons tested was activated by both 100 microM nicotine and 1 nM capsaicin. Other subsets of neurons were activated by only one of these compounds, whereas a fourth subset was not activated by either compound. At -60 mV, the magnitude of the capsaicin-activated currents was about three times larger than the magnitude of the nicotine-activated currents. The current-voltage relationship of the nAChR exhibited marked rectification, such that for voltages > or = 0 mV the current was essentially zero. In contrast, the current-voltage relationship of the capsaicin-activated current was ohmic from +/- 60 mV. These data indicate the existence of subsets of capsaicin-sensitive afferent neurons.

Simulation of Na/K Pump Current-Voltage Relationship

1992 ◽  
Vol 671 (1 Ion-Motive AT) ◽  
pp. 449-451 ◽  
Author(s):  
X.-Y. LIU ◽  
T. A. KINARD ◽  
J. R. STIMERS
Keyword(s):  
Pump Current ◽  
Current Voltage ◽  
Current Voltage Relationship ◽  
Voltage Relationship

scholarly journals Ionic Basis of Membrane Potential and of Acetylcholine-evduced Currents in the Cell Body of the Cockroach Fast Coxal Depressor Motor Neurone

1990 ◽  
Vol 151 (1) ◽  
pp. 21-39 ◽  
Author(s):  
JONATHAN A. DAVID ◽  
DAVID B. SATTELLE
Keyword(s):  
Cell Body ◽  
Outward Current ◽  
Motor Neurone ◽  
Resting Potential ◽  
Inward Current ◽  
Current Voltage ◽  
Low K ◽  
Current Voltage Relationship ◽  
Ionic Basis ◽  
Voltage Relationship

The ionic basis of the resting potential and of the response to acetylcholine (ACh) has been investigated in the cell body membrane of the fast coxal depressor motor neurone in the metathoracic ganglion of the cockroach Periplaneta americana. By means of ion-sensitive microelectrodes, intracellular concentrations of three ion species were estimated (mmoll−1): [K+]i, 1443; [Na+]i, 9±1; [Cl−], 7±1. The resting potential of continuously superfused cells was −75.6±1.9mV at 22° C. A change in resting potential of 42.0±2.5mV accompanied a decade change in [K+]o. Experiments with (10−4moll−1) ouabain, Na+ injection, low temperature (10°C) and non-superfused cells indicated the presence of an electrogenic sodium pump. Under current-clamp, the cell body membrane was depolarized by sequentially applied, ionophoretic pulses (500ms duration) of ACh. Under voltage-clamp, such doses of ACh resulted in an inward current which was abolished in low-Na+ saline. Ion-sensitive electrodes revealed an increase in [Na+]i but no change in [Cl−1]j in response to externally applied ACh. The ACh-induced current-voltage relationship was shifted in a negative direction by low-K+ saline. The AChinduced inward current was usually followed by a delayed outward current which reversed at Ek. Low-K+ saline had the same effect on this outward component as depolarizing the membrane. This suggests that the outward current component is carried by K+. The ACh-induced inward current and the delayed outward current were potentiated either when [Ca2+]i was lowered by injecting the calcium chelator BAPTA or by exposure of the cell to low-Ca2+ saline. High-Ca2+ saline reduced the inward component of the response and produced a negative shift in the AChinduced current-voltage relationship. The amplitude of the delayed outward

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