EFFECTS OF VASOPRESSIN ON SINGLE CL- CHANNELS IN THE APICAL MEMBRANE OF DISTAL NEPHRON CELLS (A6)

We have investigated how two types of Cl- channels found in sodium transporting epithelium are regulated by arginine vasopressin (AVP). 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 AVP pretreatment, the 3 pS Cl- channel was more frequently observed than the 8 pS Cl- channel. AVP increased the open probability (P-0) and single channel conductance of the 3 pS Cl- channel without significantly changing the P-0 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 P-0 and single channel conductance of 3 pS Cl- channels and (2) increases the number of 8 pS Cl- channels.