The stimulatory action of vasopressin on single Cl- channels in the apical membrane of distal nephron epithelium (A6).

A6 cells cultured on permeable supports for 10 to 14 days have two types of Cl- channels in the apical membrane that have single channel conductances of 3 and 8 pS. In cells without arginine vasopressin (AVP) pretreatment, the 3 pS Cl- channel, which was Ca(2+)-activated and had an outward rectification, was more frequently observed than the 8 pS Cl- channel, which had a linear current-voltage relationship. AVP increased the 3 pS channel's single channel conductance through an increase in the Ca(2+)-sensitivity about 100-fold and the open probability (Po) without significantly changing the Po or conductance of the 8 pS Cl- channel. On the other hand, AVP did not affect the number of the 3 pS Cl- channel, but increased the number of 8 pS Cl- channels. These observations suggest that AVP has two different pathways to increase apical membrane chloride conductance in distal nephron A6 cells; i.e., 1) increases the Po and single channel conductance of 3 pS Cl- channels and 2) increases the number of 8 pS Cl- channels.