Endothelial-derived nitric oxide inhibits sodium transport by affecting apical membrane channels in cultured collecting duct cells

Abstract

Previously, it has been shown that the addition of bradykinin (Bk) to M-1 cortical collecting duct cells in the presence of endothelial cells decreased short-circuit current (Isc), a measure of net active transport. This effect is presumably due to the release of endothelium-derived nitric oxide (EDNO), because the decrease in Isc could be blocked with Nw-nitro-L-arginine. To show that the inhibition of Isc was due to EDNO rather than prostaglandins, the ability of a cyclooxygenase inhibitor to block the inhibition was examined. When Bk was added to cocultures in the presence of meclofenamate (10-5 M), Isc decreased from 62 ± 12 to 44.5 ± 7 μA/cm2, not significantly different from that in the absence of meclofenamate. To determine if the effect was due to an alteration of sodium absorption, Bk (10-9 M) was added to cocultures, resulting in a decrease in Na flux from 28 ± 3.1 to 20 ± 2.2 nEq/min (P < 0.05), with Isc decreasing from 25 ± 2.4 to 20 ± 3.6 nEq/min (P < 0.05). To examine if the inhibition was due to blockade at the apical membrane sodium channel or the basolateral Na+/K+ ATPase, the cation-selective ionophore nystatin was used. Nystatin reversed the effect of EDNO on Isc. The effects of EDNO on Na+/K+ ATPase were also measured directly. Under maximum rate conditions, the Na+/K+ ATPase activity of control and Bktreated cocultures was 5.2 ± 0.3 and 6.8 ± 1.0 nmol/ min per square centimeter, respectively (not significantly different). EDNO also did not significantly affect the K1/2 for Na+ or K+. It was concluded that, in M-1 cortical collecting duct cells, the EDNO-induced decrease in Isc is (1) specifically due to an inhibition in Na transport and (2) this inhibition is not occurring at the Na+/K+ ATPase and therefore must occur at the apical membrane channel; also, (3) this effect does not depend on the release of prostaglandins.