Decrease in oxygen cost of contractility during hypocapnic
alkalosis in the canine hearts.
Onishi, Katsuya, Kiyotsugu Sekioka, Ryoichi Ishisu, Hideyuki Tanaka,
Mashio Nakamura, Yuji Ueda, Takeshi Nakano.
First Department of Internal Medicine, Mie University School of
Medicine, Tsu 514, Japan
APStracts 2:0478H, 1995.
The Ca2+ sensitization of the contractile machinery could
theoretically enhance the mechanoenergetics of the hearts. We studied
the effects of alkalosis, with Ca2+ sensitization, on
mechanoenergetics using the frameworks of the relationships of left
ventricular pressure-volume area (PVA; a measure of the total
mechanical energy), myocardial oxygen consumption (VO2), and the
contractility index (Emax) in ten excised, cross-circulated canine
hearts. Alkalosis was stably maintained without hypoxia (mean pH,
7.66). Alkalosis increased Emax without changing the slope of the
VO2-PVA relation, a reflected contractile efficiency. The incremental
ratio of unloaded VO2 to Emax in alkalosis was significantly lower
than by that in calcium (0.0012 +/- 0.0010 vs. 0.0062 +/- 0.0030;
p<0.01). Basal metabolism under KCl-arrest was unchanged by
alkalosis, indicating the decreased energy cost of the excitation
-contraction coupling by alkalosis. As compared to the control,
alkalosis increased Emax during the calcium 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 the Ca2+ sensitization.
Received 27 April 1995; accepted in final form 12 October 1995.
APS Manuscript Number H394-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95