The three universally accepted mechanisms of chloride transport across plasma membranes are: (i) sodium-coupled symport; (ii) anion-coupled antiport; and (iii) coupling to primary ion transport through electrical and/or chemical mechanisms. No direct evidence has been provided for primary chloride transport despite numerous reports of cellular, anion-stimulated ATPases and of chloride transport processes. Anion-stimulated ATPases are of mitochondrial origin and are a ubiquitous property of practically all animal cells. It also appears that there are other subcellular sites of anion-stimulated ATPase activity, especially the plasma membranes. Recent studies have provided indirect evidence (through parallel studies on the same tissue of anion-stimulated ATPase activity and chloride fluxes) which suggests a possible involvement of ATPase in net movement of chloride up its electrochemical gradient across plasma membranes. Further studies are required to substantiate a direct transport function to Cl--stimulated ATPases located in the plasma membrane.

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