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

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.

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

eLife ◽

10.7554/elife.25755 ◽

2017 ◽

Vol 6 ◽

Cited By ~ 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.

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

AJP Cell Physiology ◽

10.1152/ajpcell.1996.270.6.c1807 ◽

1996 ◽

Vol 270 (6) ◽

pp. C1807-C1814 ◽

Cited By ~ 43

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.

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