Whole-cell voltage- and patch-clamp techniques were used to record the calcium-dependent component of ImAHP and correlated single-channel activity in postnatal cultured rat hippocampal neurons. The Ca-dependent ImAHP was elicited by voltage steps to + 10 mV from a holding potential of -50 mV in the whole-cell mode. In cell-attached patches, single currents of approximately 2 pA were observed following spontaneous action currents. The duration of ensemble-averaged single-channel activity was very similar to that of the whole-cell ImAHP, approximately 100 ms. Both whole-cell current and single-channel activity could be blocked by bath-applied cadmium, 200 microM. Vigorous channel activity was evoked by bursts of action potentials that are known to elicit Ca-dependent AHPs. We conclude that this channel is a candidate for mediating ImAHP.