Resolution of ouabain-sensitive and extracellular K+-activated Na+ extrusion in cardiac tissue.
Intracellular sodium activity (aiNa) was measured in sheep cardiac Purkinje fibres exposed intermittently to calcium-free solutions containing 1.3 mM-Na+ with 0-16 mM-K+ and 0-0.2 mM ouabain. In potassium-free solution (O K+) mean maximum Na+ pump activity (i.e. excluding Na+ influx and Na+-Ca2+ exchange) was 61% of that in the 4 mM-K+ control solution; in 0.2mM-ouabain-4 mM-K+ it was still 44% of control. This high ouabain concentration abolished Na+ extrusion only in O K+ while reducing it by the same absolute amount at all other extracellular K+ concentrations. The Na+ pump may therefore have two independent components in cardiac tissue.
Achenbach
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Department of Physiology II, Bonn, F.R.G.
D000818:Animals; D006329:Heart Conduction System / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011690:Purkinje Fibers / Q000187:drug effects / Q000378:metabolism*; D012756:Sheep; D012964:Sodium / Q000378:metabolism*
D007473:Ion Channels; D010042:Ouabain; D012964:Sodium; D011188:Potassium