Anion-dependent sodium ion conductance of platelet plasma membranes.
External stimulate Na+ efflux from platelet plasma membrane vesicles. Efflux is apparently electrogenic since K+ diffusion potentials induced with valinomycin (interior positive) accelerate and potentials of the opposite polarity (interior negative) inhibit. In the presence of stimulatory anions, voltage-dependent Na+ efflux is much faster than Na+-Na+ exchange in the absence of an induced membrane potential. Anions stimulate voltage-dependent efflux in the following order: SCN- greater than I- greater than NO3- greater than Br- approximately acetate approximately Cl- greater than F- approximately SO42- greater than HPO42-, gluconate, and isethionate. Thiocyanate, the most stimulatory anion, increases Na+ efflux 20-fold in the presence of a membrane potential (interior positive). Stimulation of efflux by Cl- is a saturable phenomenon with a K0.5 of 41 mM and a maximal 2-3-fold stimulation over the basal level of efflux. Neither basal nor valinomycin-stimulated efflux was influenced by the presence of the platelet-aggregating agents thrombin, epinephrine, or ADP in the presence of fibrinogen.
D000818:Animals; D000838:Anions; D001693:Biological Transport, Active / Q000187:drug effects; D001792:Blood Platelets / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D012964:Sodium / Q000097:blood*; D013552:Swine
D000838:Anions; D002712:Chlorides; D007473:Ion Channels; D012964:Sodium