Chloride channels activated by hyperpolarization in Aplysia neurones

The outside-out configuration of the patch-clamp technique was used in order to characterize the elementary events underlying the previously described hyperpolarization-activated Cl current of Aplysia neurones. A few membrane patches bathed with K-free internal and external solutions showed channels characterized by long duration (up to several seconds) bursts of activity which were clearly activated by hyperpolarization. I-V curves of elementary current obtained for three different values of the Cl equilibrium potential show that these channels are selective for Cl ions. During the bursts, the current fluctuates between three levels: the resting (closed) level, a level of maximum conductance (10-15 pS) and a half-conductance level. This behaviour is similar to that of the Cl channels extracted from Torpedo electroplaques.