Endogenous vasopressin regulates Na-K-ATPase and Na+-K+-Cl− cotransporterrbsc-1 in rat outer medulla

Abstract

Previous reports have shown a stimulatory effect of vasopressin (VP) on Na-K-ATPase and rBSC-1 expression and activity. Whether these VP-dependent mechanisms are operating in vivo in physiological conditions as well as in chronic renal failure (CRF) has been less well studied. We measured ATPase expression and activity and rBSC-1 expression in the outer medulla of controls and moderate CRF rats both before and under in vivo inhibition of VP by OPC-31260, a selective V2-receptor antagonist. OPC-31260 decreased Na-K-ATPase activity from 11.2 ± 1.5 to 3.7 ± 0.8 in controls ( P < 0.05) and from 19.0 ± 0.8 to 2.9 ± 0.5 μmol Pi · mg protein−1 · h−1 in moderate CRF rats ( P < 0.05). CRF was associated with a significant increase in Na-K-ATPase activity ( P < 0.05). Similarly, CRF was also associated with a significant increase in Na-K-ATPase expression to 164.4 ± 21.5% compared with controls ( P < 0.05), and OPC-31260 decreased Na-K-ATPase expression in both controls and CRF rats to 57.6 ± 9.5 and 105.3 ± 10.9%, respectively ( P < 0.05). On the other hand, OPC-31260 decreased rBSC-I expression in both controls and CRF rats to 60.8 ± 6.5 and 30.0 ± 6.9%, respectively ( P < 0.05), and was not influenced by CRF (95.7 ± 5.2%). We conclude that 1) endogenous VP modulated Na-K-ATPase and rBSC-1 in both controls and CRF; and 2) CRF was associated with increased activity and expression of the Na-K-ATPase in the outer medulla, in contrast to the unaltered expression of the rBSC-1. The data suggest that endogenous VP could participate in the regulation of electrolyte transport at the level of the outer medulla.