Decreased sodium-potassium pump activity in isolated hypertrophied feline ventricular myocytes

Abstract

The activity of the Na-K pump was assessed in normal and hypertrophied isolated feline myocytes by measuring ouabain-sensitive 42- K uptake. Right ventricular hypertrophy was produced in feline myocardium by placing a constricting band around the pulmonary artery of adult cats. High yields of calcium tolerant myocytes were isolated from the right and left ventricle of banded and sham operated animals. Intracellular sodium (Na) and potassium (K) concentrations (mM) were not significantly different (P > 0.5) in normal (Na: 13.2 ; K: 133.4) and hypertrophied (Na: 12.3 ; K: 127.5) myocytes. Morphometric analysis demonstrated a 26% increase in width and a 42% increase in volume of hypertrophied myocytes, however, the sarcomere length (1.9 μ) was not different in both cell types. The rate constant (k, min −1) describing 42-K uptake and the calculated total K influx (I, pmol/cm 2/sec) were not significantly different (P > 0.5) in normal (k=0.059 ; I=15.9) and hypertrophied (k=0.062; I=15.3) cells. Ouabain-sensitive (active) K influx, a measure of Na-K pump activity, was maximally inhibited at 10 −4M ouabain in both cell types. At this concentration, ouabain-sensitive K uptake was decreased 23.5% in hypertrophied myocytes compared to control. The decrease in active K influx may be due to a decrease in the activity of the Na-K ATPase and/or to a reduction in the passive movement of sodium and potassium down their electrochemical gradients.