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

Using patch-clamp techniques, a Ca²⁺-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 Ba²⁺, Cs⁺ and other pharmacological agents to block the channel. The channel was highly selective for K⁺ over Na⁺ (P_Na/P_K=0.04). Channel activity, expressed as open probability (P_o), was dependent on membrane potential with depolarization increasing P_o over the physiological range in the presence of Ca²⁺. Channel activity was also dependent on cytoplasmic-side Ca²⁺. P_o was reduced to near-zero levels following EGTA chelation of Ca²⁺ in the solution bathing the cytoplasmic face of excised membrane patches; channel activity was most sensitive to changes in Ca²⁺ concentration between 10nmoll⁻¹ and 10μmoll⁻¹. 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.