ANTIDIURETIC HORMONE-RESPONDING NONSELECTIVE CATION CHANNEL IN DISTAL NEPHRON EPITHELIUM (A6)

Arginine vasotocin (AVT, 70 mU/ml) added from the basolateral side transiently activated a nonselective cation (NSC) channel with a single-channel conductance of 28.5 pS and almost identical selectivity for Na+ and K+ in the apical membrane of distal nephron cells (A6) cultured on permeable supports for 10-12 days in media containing 10% fetal bovine serum without supplemental aldosterone. The open probability (P-o) of the NSC channel at the apical resting membrane potential in cell-attached patches was similar to 0.09 and increased when the apical membrane depolarized. The P-o of the NSC channel was decreased by a rise in cytosolic Ca2+ concentration within a range of 30 nM-1 mu M but not affected by cytosolic pH within a range of 6-8. The channel was activated by the application of negative pressure (10-60 cmH(2)O) into the patch pipette. Gadolinium (2 mu M), an inhibitor of stretch-activated channels, decreased the P-o by 40%. This blocking action of gadolinium was more effective after the channel was activated by stretch, i.e., 2 mu M gadolinium decreased the P-o by 70% when a negative pressure (60 cmH(2)O) was applied into the patch pipette. Amiloride (10 and 100 mu M) showed a blocking action on the channel only when the NSC channel was activated by stretch.