ИСТИНА

This study examined the relative impact of Na+/K+-pump and Na+,K+,2Cl- cotransport in the regulation of the volume of human lung fibroblasts. Inhibition of he Na+/K+-pump by ouabain or Na+,K+,2Cl- cotransport by bumetanide attenuated the rate of K+ (86Rb influx) in human lung fibroblasts by 2-3-fold (695±14 and 522±14, respectively, vs 1537±124 cpm/well in control) whereas simultaneous addition of both inhibitors decreased the rate of K+ influx by ~8-fold (180±8 cpm/well). 24-hr inhibition of the Na+/K+-pump and Na+,K+,2Cl- cotransport did not significantly change the volume of human lung fibroblast measured as 14C-urea available space whereas simultaneous blockage of both ion transporter resulted in ~2-fold elevation of cell volume. Thus, our results demonstrates for the first time that both Na+/K+-pump and Na+,K+,2Cl- cotransport contribute to cell volume adjustment in human lung fibroblasts. They also suggest that Na+/K+-pump protects human lung fibroblast from cell volume modulation triggered by natural regulators of the Na+,K+,2Cl- cotransport. In vascular smooth muscle cells, Na+,K+,2Cl- cotransport is subjected to reciprocal regulation by [Ca2+]I and activators of cAMP- and cGMP-signaling (1;2). The role of these signaling pathways in the regulation of Na+/K+-pump and Na+,K+,2Cl- cotransport in human lung fibroblasts is currently investigated. (1) Orlov,S.N., Resink,T.J., Bernhardt,J., and Buhler,F.R. 1992. J.Membrane Biol. 126:199-210. (2) Orlov,S.N., Tremblay,J., and Hamet,P. 1996. Am.J.Physiol. 270:C1388-C1397.