Effect of vasopressin on intracellular Na+ concentration in cortical collecting duct
Breyer, M.D.; Fredin, D.
Kidney International. Supplement 57: S57-S61
1996
ISSN/ISBN: 0098-6577 PMID: 8941923 Document Number: 467552
Vasopressin stimulates transepithelial Na+ absorption in the rabbit cortical collecting duct (CCD), however, this increase is short-lived and is followed by sustained inhibition of Na+ absorption. Previous studies suggest that increased basolateral Ca-2+ influx via a Na+/Ca-2+ 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+/Ca-2+ 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 mu-M 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 Ca-2+ influx, via a Na+/Ca-2+ exchanger. This latter event could contribute to feedback inhibition of Na+ absorption in the CCD.