Fig. 1.

Voltage and calcium dependence of dendritic BK channels of HNS magnocellular neurons. A, micrograph of a recording electrode positioned on the dendrite of a dissociated SON neuron. B, time spent in the open state by two dendritic BK channels, recorded in inside-out patch-clamp configuration in the presence of 5 μM free Ca²⁺, increases as the membrane is depolarized. C, traces recorded at -40 mV in the same patch as in B show the dependence of channel activity on intracellular calcium (1–10 μM). D, plot of BK channel current amplitude as a function of membrane potential calculated from results in B. A linear fit of this relationship (r = 0.99) gave a BK channel unitary conductance of 261 pS. C and O, closed and open states, respectively. The number next to the letter O represents the number of channel(s) simultaneously open.