Transmembrane potassium fluxes in isolated feline ventricular myocytes

Radioactive tracer (42K) flux techniques were used to determine transmembrane K+ influx and efflux in isolated cardiac myocytes. Ca2+-tolerant adult feline ventricular myocytes were isolated by retrograde perfusion of the coronary arteries with a collagenase-containing solution. The isolated cells had intracellular Na+ (17.2 +/- 0.2 mM) and K+ (135.0 +/- 3.9 mM) concentrations that were stable over time. 42K influx and efflux were both described by a single exponential function. The rate constant describing 42K influx was 5.86 +/- 0.40 X 10(-2) min-1, and the calculated total K+ influx was 18.4 +/- 1.6 pmol X cm-2 X s-1. Ouabain produced a dose-dependent decrease in K+ influx with maximal inhibition at 10(-4) M. In the presence of 10(-4) M ouabain, total K+ influx was resolved into both active (ouabain-sensitive 12.2 pmol X cm-2 X s-1) and passive (ouabain-insensitive 6.2) components. The rate constant describing 42K efflux was 6.46 +/- 0.50 X 10(-2) min-1, and the calculated total K+ efflux was 22.0 +/- 1.5 pmol X cm-2 X s-1. K+ efflux was not significantly altered (P greater than 0.5) in the presence of 10(-4) M ouabain. The absolute magnitudes of total K+ influx and efflux were not significantly different (P greater than 0.1), thus suggesting that the cells were in a steady state with respect to K+. These studies demonstrate that transmembrane tracer kinetics and K+ fluxes were readily described using isolated adult cardiac myocytes and that both the active and passive components of these unidirectional fluxes were identified in the presence of ouabain.