VASOPRESSIN ACTIVATES A CHLORIDE CONDUCTANCE IN CULTURED CORTICAL COLLECTING DUCT CELLS

In rabbit cortical collecting duct (CCD) cells, arginine vasopressin ( AVP) causes a transient increase followed by a sustained depression of transepithelial potential difference (PDte). Mechanisms underlying th e decrease in PDte, are not well understood. In this study, we used pr imary cultures of rabbit CCD cells to study effects of AVP. Basolatera l addition of AVP caused a dose-dependent increase in transepithelial conductance (Gte) and a corresponding decrease in PDte,. A significant effect was observed at 1 pM AVP, and half-maximal response occurred a t 30 pM AVP; 1 nM AVP increased G(te) and decreased PDte. Replacement of apical Na+ with N-methyl-D-glucamine did not prevent the effect of AVP on G(te), suggesting that it is not mediated by an increase in api cal Na+ conductance. Similarly, apical Ba2+ (1 mM) or 4,4'-diisothiocy anostilbene-2,2'-disulfonic acid (DIDS, 0.1 mM) failed to prevent the effect of AVP. On the other hand, 5-nitro-2(3-phenylpropylamino)benzoi c acid (0.1 mM) caused partial inhibition, whereas substitution of api cal Cl- with gluconate or cyclamate almost completely prevented the AV P-induced increase in G(te). In unidirectional ion-flux studies, 1 nM AVP caused only a modest increase in apical-to-basolateral (A --> BL) flux of Na-22 and had no effect on transepithelial flux of Rb-86 in ei ther direction. On the other hand, AVP caused a pronounced increase in A --> BL flux and BL --> A flux of Cl-36, resulting in an increased n et Cl- absorption. The effect of AVP on G(te) could be mimicked by 8-b romo-adenosine 3',5'-cyclic monophosphate (8-bromo-cAMP) and isoproter enol, and effects of AVP and isoproterenol were not additive. These da ta indicate that in rabbit CCD cells AVP activates a DIDS-insensitive Cl- conductance via cAMP, Similarities between responses to AVP and is oproterenol, which increases cAMP in intercalated cells only, suggest that the effect of AVP on Cl- conductance takes place, at least in par t, in intercalated cells.