Abstract
Ion channels in the apical membrane of cultured mouse renal collecting tubule cells were investigated using the patch-clamp technique. At least two types of ion channels were observed with cell-attached patches under control conditions. One was an inwardly rectifying small conductance (20-30 pS) K channel (SK channel) and the other was an intermediate conductance (40-50 pS) non-selective cation channel (NC channel). Activity of the SK channel was relatively high, whereas that of NC channels was usually low in the control condition. Addition of membrane-permeant cAMP analogue, 8Br-cAMP (100 μM), stimulated the activity of SK channels but did not affect that of NC channels in inside-out patches. In the presence of 1mM Ca2+, addition of Ca2+-ionophore, ionomycin (1 μM), resulted in marked enhancement of NC channel activity and reduction of SK channel activity. In inside-out patches, SK channels required cytosolic ATP (1 mM) to maintain their activity, which was not affected by cytosolic Ca2+. On the other hand, NC channel was activated directly by elevation of cytosolic Ca2+, but not by ATP in inside-out patches. These results suggest that regulatory mechanisms of these channels are quite different, which may play a role in the electrolyte transport along the collecting duct under various conditions. [J Physiol Sci. 2006;56 Suppl:S141]
