The effect of voltage on the time course of end-plate currents.
1. End-plate currents have been studied in glycerol-treated frog sartorius nerve-muscle preparations with the voltage clamp technique.2. End-plate currents follow a simple exponential time course over most of their declining phase.3. The rate constant alpha that characterizes this exponential decay depends upon membrane potential V according to the relationship alpha (V) = Be(AV), with A = 0.00795 +/- 0.00043 (S.E.) mV(-1) and B = 1.67 +/- 0.04 (S.E.) msec(-1).4. Voltage sensitivity decreases (that is, A in the above equation becomes smaller) as the recording and current-passing electrodes are moved away from the end-plate region.5. The voltage sensitivity of alpha is decreased by decreasing the gain of the voltage clamp amplifier.6. Changing the end-plate current amplitude by curare treatment, by increased calcium ion concentration, and by facilitation and depression has essentially no effect on end-plate current time course.7. When membrane potential is changed step-wise during the decaying phase of the end-plate conductance change, currents begin to decline with a rate constant alpha appropriate to the new membrane potential in less than 0.2 msec.8. Treatment with prostigmine methylsulphate in concentrations up to 50 mug/ml. slows end-plate current decay but has little effect on voltage sensitivity. That is, B in the above equation is decreased by prostigmine treatment, but A is relatively unaffected.
D000200:Action Potentials; D000818:Animals; D001001:Anura; D001692:Biological Transport; D002118:Calcium / Q000494:pharmacology; D002800:Cholinesterase Inhibitors; D003472:Curare / Q000494:pharmacology; D004558:Electric Stimulation; D004594:Electrophysiology; D066298:In Vitro Techniques; D008564:Membrane Potentials; D008954:Models, Biological; D009119:Muscle Contraction; D009388:Neostigmine / Q000494:pharmacology; D009431:Neural Conduction; D009469:Neuromuscular Junction / Q000502:physiology*; D011188:Potassium; D011894:Rana pipiens; D012964:Sodium; D013997:Time Factors
D002800:Cholinesterase Inhibitors; D009388:Neostigmine; D003472:Curare; D012964:Sodium; D011188:Potassium; D002118:Calcium