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Decreased sodium-potassium pump activity in isolated hypertrophied feline ventricular myocytes
Insights
The sodium-potassium (Na-K) pump activity was reduced in hypertrophied feline heart cells. This suggests altered ion transport in cardiac hypertrophy, impacting heart function.
Area of Science:
- Cardiovascular Physiology
- Cellular Biology
- Biochemistry
Background:
- Cardiac hypertrophy involves changes in myocyte structure and function.
- The Na-K pump is crucial for maintaining cellular ion balance and membrane potential.
- Understanding Na-K pump activity in hypertrophy is vital for cardiac health.
Purpose of the Study:
- To investigate the activity of the Na-K pump in normal and hypertrophied feline cardiac myocytes.
- To determine if cardiac hypertrophy affects intracellular sodium and potassium concentrations.
- To assess the impact of hypertrophy on the rate and extent of potassium uptake.
Main Methods:
- Inducing right ventricular hypertrophy in cats using pulmonary artery constriction.
- Isolating calcium-tolerant myocytes from ventricles of control and banded animals.
- Measuring 42-K uptake to assess Na-K pump activity, with and without ouabain inhibition.
- Performing morphometric analysis to quantify changes in myocyte size and sarcomere length.
Main Results:
- Intracellular Na and K concentrations were not significantly different between normal and hypertrophied myocytes.
- Hypertrophied myocytes showed increased width and volume but unchanged sarcomere length.
- Total potassium influx was similar, but ouabain-sensitive (active) K influx decreased by 23.5% in hypertrophied cells.
- The decrease in active K influx may indicate reduced Na-K ATPase activity or altered ion gradients.
Conclusions:
- Cardiac hypertrophy in feline myocytes is associated with a reduced Na-K pump activity.
- Despite similar total K influx, the active component mediated by the Na-K pump is diminished.
- These findings suggest potential alterations in ion homeostasis contributing to the pathophysiology of cardiac hypertrophy.
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 greater than 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 mu) 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/cm2/sec) were not significantly different (P greater than 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(-4)M 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.