EFFECT OF NA+ AND K+ ON CL- DISTRIBUTION IN GUINEA-PIG VAS-DEFERENS SMOOTH-MUSCLE - EVIDENCE FOR NA+, K+, CL- COTRANSPORT

1. Smooth muscle cells of the guinea‐pig vas deferens after Cl‐ depletion actively reaccumulate ions to a level many times higher than that predicted by a passive distribution, even when anion exchange (largely responsible for Cl‐ movements in this preparation) is inhibited by DIDS (4,4'‐diisothiocyanostilbene‐2,2'‐disulphonic acid). The cells therefore must possess a second mechanism for Cl‐ accumulation. We have now investigated the ionic requirement of this mechanism using a combination of ion analysis, 36Cl fluxes and direct measurement of the intracellular Cl‐ activity (aiCl). 2. In the steady state, the Cl‐ content of tissues was 12‐16% less in Na(+)‐free solution than in normal Krebs solution. 3. Loss of 36Cl into Cl(‐)‐free solution was slowed by the absence of Na+ and accelerated on its readdition. Uptake of 36Cl by Cl(‐)‐depleted tissues was also reduced in the absence of extracellular Na+, particularly at longer time intervals as uptake reached completion. These effects occurred in the presence and absence of CO2‐HCO3‐ and in the presence of DIDS. 4. The initial rate of rise of aiCl on readdition of Cl‐ to Cl(‐)‐depleted cells was not significantly affected by the absence of Na+ in the presence of a functional anion exchange, but aiCl stabilized at a lower value than in normal solution. Readdition of Na+ stimulated a rise in aiCl to the control level. Removal and readdition of K+ under these conditions had negligible effects. 5. When anion exchange was inhibited by the presence of DIDS, removal and readdition of Na+ caused, respectively, a marked inhibition and stimulation of the rise in aiCl during Cl‐ reaccumulation. Under these conditions removal and readdition of K+ had similar effects. 6. The results suggest that Na+, K+, Cl‐ co‐transport is involved in transmembrane movements of Cl‐ at least when the anion exchange mechanism is blocked. 7. The possibility that the marked effects of changes in external Na+ on transmembrane Cl‐ movements in the presence of a functional anion exchange mechanism are caused by secondary effects due to changes in intracellular pH as well as to suppression of Na+, K+, Cl‐ co‐transport is discussed. © 1990 The Physiological Society