Voltage clamp analysis of the kinetics of piperidine-induced chloride current in isolated Aplysia neurons

Abstract

The effect of piperidine (Pip) on isolated Aplysia neurons was investigated using the voltage clamp and concentration clamp techniques in which neurons were perfused internally and externally with Na+,K+ free solution. Pip induced a Cl-current (ICl) in a dose-dependent manner for doses ranging from 10(-4) M to 10(-2) M. The dose-response curve gave an apparent dissociation constant of 8.4 x 10(-4) M and a Hill coefficient of 1.7. The current-voltage relationship was linear in the voltage range examined (-70 to +30 mV). The equilibrium potential for Pip induced current was close to the calculated equilibrium potential for chloride ions (ECl), (-10.7 mV). The activation phase of the ICl was characterized by a single exponential at all concentrations. The time constant of this phase decreased with increasing concentrations of Pip but did not depend on the membrane potential. The deactivation phase of the ICl proceeded on a single exponential curve at concentrations of Pip less than 5 x 10(-4) M, but on a double exponential at concentrations of 5 x 10(-4) M and higher. The deactivation time constant also decreased with increasing concentrations of Pip, but showed no potential dependence. Pip- and ACh-induced IClS were not blocked by 10(-4) M atropine. However, Pip-induced ICl was abolished with 10(-4) M d-tubocurarine (dTC), and the ACh-induced ICl was depressed by the same dose of dTC. These results suggest that Pip acts on at least two components of the nicotinic receptor-Cl channel complex in Aplysia neurons to elicit the ICl.