Effects Of Atrophy On Cardiac Potassium Channels In Transplanted Rat Myocytes

BACKGROUND AND OBJECTIVESMany studies have demonstrated a correlation between cardiac hypertrophy and a structural and functional change of myocytes. The effect of unloading and atrophy have recently become of more interest since device for mechanical left ventricular unloading have been introduced into clinical cardiac atrophy on cardiac K⁺ currents has not been studied. Heterotopic, vascularized, but non-working mice hearts 5 days after transplantation undergo atrophy and have reduced contractile activity.METHODCells were isolated from rejecting, allogeneic and non-rejecting, syngeneic transplanted hearts. The effects of transplantation on cell size and potassium currents,including the transient outward K⁺ current (I_to), sustained outward current (I_sus) and inward rectifier K⁺ current (I_k1) were determined.RESULTS AND CONCLUSION1. Cell capacitance was unchanged, but cell volume was reduced by 35% in cells isolated from transplanted hearts, consistent with atrophy and loss of myofibrillar mass.2. Action potential amplitude of transplant myocytes was not significantly different, but the resting membrane potential was reduced and action potential duration was prolonged compared to control myocytes.3. The prolonged action potentials were associated with a decrease in I_to, I_sus, and I_k1 in myocytes isolated from rejecting, allogeneic transplants, and a decrease in I_sus in myocyctes isolated from non-rejecting syngeneic transplants.