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Am J Physiol Heart Circ Physiol 270: H1905-H1913, 1996;
0363-6135/96 $5.00
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AJP - Heart and Circulatory Physiology, Vol 270, Issue 6 1905-H1913, Copyright © 1996 by American Physiological Society

ARTICLES

Decrease in oxygen cost of contractility during hypocapnic alkalosis in canine hearts

K. Onishi, K. Sekioka, R. Ishisu, H. Tanaka, M. Nakamura, Y. Ueda and T. Nakano
First Department of Internal Medicine, Mie University School of Medicine, Tsu, Japan.

Ca2+ sensitization of contractile machinery could theoretically enhance the mechanoenergetics of the heart. We studied the effects of alkalosis with Ca2+ sensitization on mechanoenergetics within the framework of the relationships of left ventricular pressure-volume area (PVA; a measure of the total mechanical energy), myocardial oxygen consumption per beat (VO2), and the contractility index [E(max) (slope of end-systolic pressure-volume relation)] in 10 excised, cross-circulated canine hearts. Alkalosis was stably maintained without hypoxia (mean pH 7.66). Alkalosis increased E(max) without changing the slope of the VO2-PVA relation, a reflected contractile efficiency. The incremental ratio of unloaded VO2 to E(max) in alkalosis was significantly lower than that in Ca2+ sensitization (0.0012 +/- 0.0010 vs. 0.0062 +/- 0.0030 ml O2 . mmHg-1 . ml . beat-1 . 100 g LV-2; P < 0.01). Basal metabolism under KCl arrest was unchanged by alkalosis, indicating the decreased energy cost of the excitation-contraction coupling by alkalosis. Compared with the control, alkalosis increased E(max) during the Ca2+ infusion of various concentrations without any further increase in unloaded VO2. Thus we demonstrated a decreased oxygen cost of contractility during alkalosis, presumably due to Ca2+ sensitization.


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