AJP - Heart and Circulatory Physiology, Vol 259, Issue 4 1044-H1049, Copyright © 1990 by American Physiological Society

ARTICLES

Effect of acidosis on contractile system in skinned fibers of hypertrophied rat heart

S. Kimura, A. L. Bassett, T. Furukawa, N. Furukawa and R. J. Myerburg
Department of Medicine (Division of Cardiology), University of Miami School of Medicine 33101.

Hypertrophied hearts have enhanced susceptibility to ischemia-induced contractile dysfunction. To explore the mechanisms of this phenomenon, we studied the effect of acidosis on the Ca2+ sensitivity of the contractile proteins and on Ca2+ accumulation by the sarcoplasmic reticulum (SR) in chemically (saponin) skinned cardiac fibers obtained from normal and pressure-overloaded hypertrophied rat left ventricles. Left ventricular pressure overload was induced by partial ligation of the abdominal aorta 6-8 wk before study. Age- and weight-matched normal rats served as controls. Pressure overload increased the left ventricular weight-to-body weight ratio by 48%. Reduction in pH shifted the pCa-tension curve to the right similarly in normal and hypertrophied preparations, and there was no difference in pCa-tension relationship at pH 7.0 or 6.5 between the two groups. However, reducing the pH of 1 microM Ca2(+)-loading solution from 7.0 to 6.5 decreased the amount of Ca2+ accumulated in the SR to 66.2 +/- 3.0% in normal fibers and 43.2 +/- 4.0% in hypertrophied fibers (P less than 0.01). We conclude that the enhanced susceptibility of hypertrophied hearts to ischemia-induced diastolic dysfunction may be partly explained by the greater depressing effect of acidosis on Ca2+ accumulation by the SR.

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