Modulation of the endogenous electrical activity of the bursting neuron in the snail Helix pomatia—II. The membrane characteristics related to modulation of the endogenous activity of the neuron

Abstract

The relation of the amplitude of the slow inward current to the holding potential and the changes of membrane conductance during the development of the slow inward current under voltage clamp conditions were investigated on neurons RPa1 and RPa7. The amplitude of the slow inward current in neuron RPa1 linearly increased with membrane hyperpolarization from −30 to −90 mV. The equilibrium potential for the slow inward current found by extrapolation was about +45 mV. In neuron RPa1 rectangular hyperpolarizing pulses (7 mV, 2s), applied from a holding potential of −60 mV, evoked inward currents before the development of the slow inward current and outward currents at the maximum of the slow inward current. These currents decreased with time. In the neuron RPa7 no relation of the amplitude of the slow inward current to holding potentials between −58 and −78 mV and no changes of membrane conductance during the development of the slow inward current were found. It is concluded that the slow inward current in neuron RPa1 is due to an increase of the membrane's sodium permeability. During the development of the slow inward current an additional potential- and time-dependent increase in permeability occurs upon hyperpolarization, obviously to potassium or chloride ions.