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 typ es of Cl- channels in the apical membrane that have single channel con ductances of 3 and 8 pS. In cells without arginine vasopressin (AVP) p retreatment, the 3 pS Cl- channel, which was Ca2+-activated and had an outward rectification, was more frequently observed than the 8 pS Cl- channel, which had a linear current-voltage relationship. AVP increas ed the 3 pS channel's single channel conductance through an increase i n the Ca2+-sensitivity about 100-fold and the open probability (P-0) w ithout significantly changing the P-0 or conductance of the 8 pS Cl- c hannel. On the other hand, AVP did not affect the number of the 3 pS C l- channel, but increased the number of 8 pS Cl- channels. These obser vations suggest that AVP has two different pathways to increase apical membrane chloride conductance in distal nephron A6 cells; i.e., 1) in creases the P-0 and single channel conductance of 3 pS Cl- channels an d 2) increases the number of 8 pS Cl- channels.