Properties and function of KCNQ1 K+ channels isolated from the rectal gland of Squalus acanthias

KCNQ1 (K(V)LQT1) K+ channels play an important role during electrolyte secr etion in airways and colon. KCNQ1 was cloned recently from NaCl-secreting s hark rectal glands. Here we study. the properties and regulation of the clo ned sK(V)LQT1 expressed in Xenopus oocytes and Chinese hamster ovary (CHO) cells and compare the results with those obtained from in vitro perfused re ctal gland tubules (RGT). The expression of sKCNQ1 induced voltage-dependen t, delayed activated K+ currents, which were augmented by an increase in in tracellular cAMP and Ca2+. The chromanol derivatives 293B and 526B potently inhibited sKCNQ1 expressed in oocytes and CHO cells, but had little effect on RGT electrolyte transport. Short-circuit currents in RGT were activated by alkalinization and were decreased by acidification. In CHO cells an alk aline pH activated and an acidic pH inhibited 293B-sensitive KCNQ1 currents . Noise analysis of the cell-attached basolateral membrane of RGT indicated the presence of low-conductance (<3 pS) K+ channels, in parallel with othe r K+ channels. sKCNQ1 generated similar small-conductance K+ channels upon expression in CHO cells and Xenopus oocytes. The results suggest the presen ce of low-conductance KCNQ1 K+ channels in RGT, which are probably regulate d by changes in intracellular cAMP, Ca2+ and pH.