Inward and delayed outward membrane currents in isolated neural somata under voltage clamp.

1. Membrane current-voltage relationships were investigated under voltage clamp conditions in isolated neural somata of marine gastropods.2. Step depolarizations from the resting potential produce an initial inward current followed by a delayed outward current.3. Inward current appears to be carried by both sodium and calcium ions and displays time and voltage dependent properties similar to those of other excitable membranes.4. Activation and deactivation of the delayed outward current follow a more complicated time course than that of a single exponential raised to a power but can be fitted by the product of two exponential functions.5. Delayed outward current inactivation proceeds with a time constant which decreases as membrane voltage is made more positive. The steady-state levels of inactivation as a function of membrane voltage are related by an S-shaped curve similar to that for K inactivation in squid giant axon.