Identification of a Basolateral Membrane Potassium Channel from Teleost Intestinal Epithelial Cells

Using patch-clamp techniques, a Ca-dependent, voltage-gated K channel [K(Ca) channel] was isolated from the basolateral membrane of NaCl-absorbing intestinal epithelial cells of the goby Gillichthys mirabilis. This K(Ca) channel had a high conductance (approximately 150 pS) in the physiological range of membrane potential. Conclusive identification as a K channel is supported by dependence of the reversal potential for single-channel current on the K concentration gradient and the ability of Ba, Cs and other pharmacological agents to block the channel. The channel was highly selective for K over Na (^Na/^K=0-04). Channel activity, expressed as open probability (Po), was dependent on membrane potential with depolarization increasing Po over the physiological range in the presence of Ca. Channel activity was also dependent on cytoplasmic-side Ca. Po was reduced to near-zero levels following EGTA chelation of Ca in the solution bathing the cytoplasmic face of excised membrane patches; channel activity was most sensitive to changes in Ca concentration between lOnmoll" and lO/mioll". This K(Ca) channel may be one of several avenues for K exit across the basolateral cell membrane and, as such, may play roles in both transepithelial salt transport and maintenance of intracellular ionic composition.