Effect of vasopressin on intracellular Na+ concentration in cortical collecting duct

Vasopressin stimulates transepithelial Na+ absorption in the rabbit cortical collection duct (CCD), however, this increase is short-lived and is followed by sustained inhibition of Na+ absorption. Previous studies suggest that increased basolateral Ca2+ influx via a Na+/Ca2+ exchanger may be involved in feedback inhibition of Na+ absorption, accounting for this transient stimulation. The present studies used the Na+ sensitive dye, SBFI, to measure intracellular NA+ ([Na+]i) in the CCD to determine whether either vasopressin or 3'5'cAMP increase cell Na+ in the CCD, thereby increasing Na+/Ca2+ exchange. Resting CCD [Na+]i was 23 +/- 2.5 mM. Both arginine vasopressin (AVP, 23 pM) and 0.1 mM 8-chlorophenylthio-cAMP (8CPTcAMP) transiently increased [Na+]i, which peaked within approximately 250 seconds of their addition and then gradually fell towards baseline. AVP increased [Na+]i from 19.4 +/- 3.6 to a peak of 44.4 +/- 14 mM and 8CPTcAMP increased [Na+]i from 11.8 +/- 3.6 to a peak of 38.7 +/- 6.2 mM. This [Na+]i increase was completely blocked by luminal Na+ removal. Inhibition of the basolateral Na/K ATPase with 10 microM ouabain caused [Na+]i to increase to 71.8 +/- 11.6 mM. These results demonstrate that cAMP and AVP increase CCD [Na+]i via a mechanism involving enhanced luminal Na+ entry. This [Na+]i increase is transient and of sufficient magnitude to enhance basolateral Ca2+ influx, via a Na+/Ca2+ exchanger. This latter event could contribute to feedback inhibition of Na+ absorption in the CCD.