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+ (PNa/PK=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 Ca2+. Channel activity was also dependent on cytoplasmic-side Ca2+. Po 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.

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