Calcium-activated potassium channels recorded from rat neocortical neurons in cell culture

Rat neocortical neurons in cell culture were studied with the patch-clamp technique in order to determine the properties of a large-conductance K+ channel in excised inside-out patches. In the presence of a physiological ionic gradient for K+ across the patch membrane ([K+]i = 120 mM; [K+]o = 3 mM), outward channel activity was detected when the patches were brought to membrane potential values less negative than -30 mV. Depolarization of the membrane increased the magnitude of the current. The I-V relationship displayed rectification at negative membrane potentials. When the I-V curve was differentiated the slope conductance calculated at 0 mV membrane potential was 120 pS. The single-channel permeability was 5.2 x 10(-13) cm/s and the current flow through the open K+ channel could be modeled using the constant-field electrodiffusion theory. K+ channel opening was not observed following removal of Ca2+ from the intracellular surface of the membrane. Our experiments indicate that, as in other cell types, rat neocortical neurons in culture exhibit a large-conductance K+ channel which is activated by Ca2+ acting on the cytoplasmic surface.