Effect of Na+ and K+ on Cl- distribution in guinea-pig vas deferens smooth muscle: evidence for Na+, K+, Cl- co-transport.
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.
University Department of Pharmacology, Oxford.
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Aickin
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Brading
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D013997:Time Factors
D001639:Bicarbonates; D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D011188:Potassium