Potassium channels in the basolateral membrane of the rectal gland ofSqualus acanthias

The present study examines the influences of pH and Ca²⁺ and several putative inhibitors on the basolateral K⁺ channel of the rectal gland ofSqualus acanthias. Excised membrane patches were examined using the patch clamp technique. It is shown that reduction of the calcium activity on the cytosolic side to less than 10^–9 mol/l has no detectable inhibitory effect on this channel. Conversely, increase in calcium activity to some 10^–3 mol/l reduced the activity of this channel. Variations in cytosolic pH had only a moderate effect on the current amplitude: alkalosis by one pH unit increased and acidosis reduced the single current amplitude by some 15%. Several inhibitors were tested in excised patches when added to the cytosolic side. Ba²⁺ (5·10^–3 mol/l), quinine (10^–3 mol/l), quinidine (10^–4 mol/l), lidocaine (1 mmol/l), tetraethylammonium (10 mmol/l), Cs⁺ (10 mmol/l), and Rb⁺ (20 mmol/l) all blocked this K⁺ channel reversibly. We conclude that the basolateral K⁺ channel of the rectal gland is distinct from other epithelial K⁺ channels inasmuch as it is not stimulated by Ca²⁺ directly, but that it is qualitatively similar to many other known K⁺ channels with respect to its sensitivity towards blockers.This study was supported by Deutsche Forschungsgemeinschaft Gr 480/8 and by NSF and NIH grants to the Mount Desert Island Biological Laboratory