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 tra nsporting epithelium are regulated by arginine vasopressin (AVP). A6 c ells cultured on permeable supports for 10 to 14 days have two types o f Cl- channels in the apical membrane that have single channel conduct ances of 3 and 8 pS. In cells without AVP pretreatment, the 3 pS Cl- c hannel was more frequently observed than the 8 pS Cl- channel. AVP inc reased the open probability (P-0) and single channel conductance of th e 3 pS Cl- channel without significantly changing the P-0 or conductan ce 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- c hannels. These observations suggest that AVP has two different pathway s to increase apical membrane chloride conductance in distal nephron A 6 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.