Switching Between Two Types of Bursting Activity of Single Ca⁺²‐Activated K⁺ Channels in Dissociated Neurons

Single channel recordings of Ca²⁺‐activated K⁺ currents were made from dissociated cockroach neurons by means of the gigaohm‐seal patch‐clamp technique. Bursts of single channel openings were composed of two distinct classes: the ‘long‐open burst’ contained groups of long, rectangular, pulse‐like openings with durations of 3.5 to 1.2 ms (depending on membrane potential), whereas the ‘flickering burst’ consisted of clusters of brief openings with an average duration of 0.4 ms (voltage‐independent) separated by short closings with a duration of about 1.0 ms. The long‐open burst and the flickering burst appeared to reflect distinct states of a single Ca²⁺‐activated K⁺ channel because direct transitions between these two types of burst were often detected. We present a kinetic scheme for the gating activation pathway of a neuronal Ca²⁺‐activated K⁺ channel, based on these findings.