scholarly journals Action Potentials in Rhodnius Oocytes: Repolarization is Sensitive to Potassium Channel Blockers

1986 ◽  
Vol 126 (1) ◽  
pp. 119-132
Author(s):  
M. J. O'DONNELL
Keyword(s):  
Potassium Channel ◽  
Action Potentials ◽  
Potassium Conductance ◽  
Channel Blockers ◽  
Calcium Dependent ◽  
Outward Rectification ◽  
Current Voltage ◽  
Potassium Channel Blockers ◽  
Potassium Conductances ◽  
Voltage Dependent

Depolarization of Rhodnius oocytes evokes action potentials (APs) whose rising phase is calcium-dependent. The ionic basis for the repolarizing (i.e. falling) phase of the AP was examined. Addition of potassium channel blockers (tetraethylammonium, tetrabutylammonium, 4-aminopyridine, atropine) to the bathing saline increased the duration and overshoot of APs. Intracellular injection of tetraethyl ammonium had similar effects. These results suggest that a voltage-dependent potassium conductance normally contributes to repolarization. Repolarization does not require a chloride influx, because substitution of impermeant anions for chloride did not increase AP duration. AP duration and overshoot actually decreased progressively when chloride levels were reduced. Current/voltage curves show inward and outward rectification, properties often associated with potassium conductances. Outward rectification was largely blocked by external tetraethylammonium. Possible functions of the rectifying properties of the oocyte membrane are discussed.

Effects of Octopamine on Calcium Action Potentials in Insect Oocytes

1989 ◽  
Vol 142 (1) ◽  
pp. 115-124
Author(s):  
M. J. O'DONNELL ◽  
B. SINGH
Keyword(s):  
Action Potentials ◽  
Rank Order ◽  
Potassium Conductance ◽  
Membrane Resistance ◽  
Threshold Concentration ◽  
Resting Potential ◽  
Calcium Dependent ◽  
Octopamine Receptors ◽  
Voltage Dependent ◽  
Maximum Rate Of Rise

Our experiments show that octopamine receptors are present on the developing follicles of an insect, Rhodnius prolixus. Application of D,L-octopamine decreased the duration and overshoot of calcium-dependent action potentials (APs), and increased the intrafollicular concentration of cyclic AMP. The threshold concentration of D,L-octopamine for the reduction in electrical excitability was between 1 and 5×10−7moll−1, and maximal effects of a 40–50% reduction in AP overshoot and duration were apparent at 10−4moll−1. At concentrations above 10−5moll−1, a small (<10%) hyperpolarization of the resting potential was also apparent. Effects of D,L-octopamine on oocyte excitability were independent of these small shifts in resting potential. Current injection experiments, in which calcium entry was blocked by cobalt, demonstrated that D,L-octopamine reduced membrane resistance at both hyperpolarizing and depolarizing potentials. Octopamine did not affect the maximum rate of rise of the AP, dV/dtmax, which is an indicator of inward calcium current. It is suggested that octopamine may mediate its effects on excitability through an increase in a voltage-dependent potassium conductance. Application of other phenolamines indicated a rank order of potency of D, Loctopamine > D,L-synephrine > tyramine. The α-adrenergic agonists clonidine, naphazoline and tolazoline were without significant effect at 10−5-10−3moll−1. Reduction of excitability by D,L-octopamine was effectively blocked by phentolamine and metoclopramide. Yohimbine and gramine were less effective as antagonists. Possible functions of octopamine receptors in insect follicles are discussed.

Mechanism of long-lasting synaptic inhibition in Aplysia neuron R15

1980 ◽  
Vol 44 (6) ◽  
pp. 1148-1160 ◽  
Author(s):  
W. B. Adams ◽  
I. Parnas ◽  
I. B. Levitan
Keyword(s):  
Action Potentials ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Short Exposure ◽  
Ion Conductance ◽  
Current Voltage ◽  
Voltage Dependent ◽  
Aplysia Neuron ◽  
Reversible Component ◽  
Stimulation Of

1. Long-lasting inhibition is a synaptically mediated response found in certain molluscan nerve cells that fire action potentials in bursts. It is elicited by repetitive stimulation of a presynaptic nerve and may last for minutes or hours after stimulation. 2. Voltage-clamp techniques were employed to measure the voltage dependence of the synaptically elicited current. Current-voltage curves were obtained by stepping or sweeping the voltage over the range -40 to -120 mV. 3. Long-lasting inhibition was found to be mediated by two separate conductance mechanisms. A component that reverses near -80 mV is most prominent at times up to 5 min following stimulation. A component with no reversal potential between -40 and -120 mV predominates at later times. 4. The reversible component is attenuated by reducing the intensity of stimulation of the presynaptic nerve, by injection of TEA into the postsynaptic cell, or by activation of a potassium conductance with serotonin prior to stimulation of the nerve. Thus, the reversible component appears to be mediated by an increase in potassium conductance. 5. The effects of the nonreversible component measured in the soma appear to be too large to attribute it to a conductance change that is electrically "distant" from the soma. It is attenuated by turning off a resting inward ion conductance with dopamine prior to stimulation of the nerve. It is not affected by short exposure to ouabain, but is attenuated by longer exposures that reduce the sodium and calcium gradients. Thus, the nonreversible component may be mediated by a decrease in voltage-dependent inward current flow carried by sodium or calcium.

Proteinase inhibitor homologues as potassium channel blockers

1994 ◽  
Vol 1 (4) ◽  
pp. 246-250 ◽  
Author(s):  
Jean-Marc Lancelin ◽  
Marie-Françoise Foray ◽  
Marc Poncin ◽  
Michelle Hollecker ◽  
Dominique Marion
Keyword(s):  
Potassium Channel ◽  
Proteinase Inhibitor ◽  
Channel Blockers ◽  
Potassium Channel Blockers

Calcium-dependent potassium conductance in rat supraoptic nucleus neurosecretory neurons

1985 ◽  
Vol 54 (6) ◽  
pp. 1375-1382 ◽  
Author(s):  
C. W. Bourque ◽  
J. C. Randle ◽  
L. P. Renaud
Keyword(s):  
Time Constant ◽  
Action Potentials ◽  
Supraoptic Nucleus ◽  
Potassium Conductance ◽  
Reversal Potential ◽  
Input Resistance ◽  
Mean Amplitude ◽  
Progressive Increase ◽  
Calcium Dependent ◽  
Neurosecretory Neurons

Intracellular recordings of rat supraoptic nucleus neurons were obtained from perfused hypothalamic explants. Individual action potentials were followed by hyperpolarizing afterpotentials (HAPs) having a mean amplitude of -7.4 +/- 0.8 mV (SD). The decay of the HAP was approximated by a single exponential function having a mean time constant of 17.5 +/- 6.1 ms. This considerably exceeded the cell time constant of the same neurons (9.5 +/- 0.8 ms), thus indicating that the ionic conductance underlying the HAP persisted briefly after each spike. The HAP had a reversal potential of -85 mV and was unaffected by intracellular Cl- ionophoresis of during exposure to elevated extracellular concentrations of Mg2+. In contrast, the peak amplitude of the HAP was proportional to the extracellular Ca2+ concentration and could be reversibly eliminated by replacing Ca2+ with Co2+, Mn2+, or EGTA in the perfusion fluid. During depolarizing current pulses, evoked action potential trains demonstrated a progressive increase in interspike intervals associated with a potentiation of successive HAPs. This spike frequency adaptation was reversibly abolished by replacing Ca2+ with Co2+, Mn2+, or EGTA. Bursts of action potentials were followed by a more prolonged afterhyperpolarization (AHP) whose magnitude was proportional to the number of impulses elicited (greater than 20 Hz) during a burst. Current injection revealed that the AHP was associated with a 20-60% decrease in input resistance and showed little voltage dependence in the range of -70 to -120 mV. The reversal potential of the AHP shifted with the extracellular concentration of K+ [( K+]o) with a mean slope of -50 mV/log[K+]o.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane Properties Related to the Firing Behavior of Zebrafish Motoneurons

2003 ◽  
Vol 89 (2) ◽  
pp. 657-664 ◽  
Author(s):  
Robert R. Buss ◽  
Charles W. Bourque ◽  
Pierre Drapeau
Keyword(s):  
Action Potential ◽  
Action Potentials ◽  
Membrane Conductance ◽  
Membrane Properties ◽  
High Threshold ◽  
Calcium Dependent ◽  
Larval Zebrafish ◽  
Plateau Potential ◽  
Potassium Conductances ◽  
Action Potential Burst

The physiological and pharmacological properties of the motoneuron membrane and action potential were investigated in larval zebrafish using whole cell patch current-clamp recording techniques. Action potentials were eliminated in tetrodotoxin, repolarized by tetraethylammonium (TEA) and 3,4-diaminopyridine (3,4-AP)-sensitive potassium conductances, and had a cobalt-sensitive, high-threshold calcium component. Depolarizing current injection evoked a brief (approximately 10–30 ms) burst of action potentials that was terminated by strong, outwardly rectifying voltage-activated potassium and calcium-dependent conductances. In the presence of intracellular cesium ions, a prolonged plateau potential often followed brief depolarizations. During larval development (hatching to free-swimming), the resting membrane conductance increased in a population of motoneurons, which tended to reduce the apparent outward rectification of the membrane. The conductances contributing to action potential burst termination are hypothesized to play a role in patterning the synaptically driven motoneuron output in these rapidly swimming fish.

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