Submitted on November 13, 2003
Accepted on February 19, 2004
Oxygen consumption of mechanically unloaded contractions of mouse left ventricular myocardial slices
Daisuke Yamashita1, Hisaharu Kohzuki1, Yutaka Kitagawa1, Tamiji Nakashima2, Akio Kikuta2, and Miyako Takaki1*
1 Department of Physiology II, Nara Medical University, Kashihara, Nara, Japan
2 Department of Anatomy, School of Medicine University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan
* To whom correspondence should be addressed. E-mail: mtakaki{at}naramed-u.ac.jp.
Left ventricular (LV) myocardial slices were isolated from murine hearts (300-µm thick) and were stimulated at 1Hz without external load. Mean myocardial slice oxygen consumption per minute (mVO2) without stimulation was 0.97 ± 0.14 ml 0>2.min-1.100 g LV-1 and mean mVO2 with stimulation increased to 1.80 ± 0.17 ml O2.min-1.100 g LV-1 in normal Tyrode solution. Mean delta mVO2 (=the mVO2 with stimulation - the mVO2 without stimulation) was 0.83 ± 0.12 ml O2.min-1.100 g LV-1. There were no differences between mean mVO2 with and without stimulation in Ca2+ free solution. The increases in extracellular Ca2+ concentrations up to 14.4 mM did not affect the mVO2 without stimulation, but significantly increased the mVO2 with
stimulation up to 140% of control. The delta mVO2 significantly increased up to 190% of the control in a dose-dependent manner. In contrast, the shortening did not increase in a dose-dependent manner. Cyclopiazonic acid (CPA) 30 µM significantly reduced the delta mVO2 to 0.27 ± 0.06 ml O2.min-1.100 g LV-1 (35% of control). The combination of 5 mM 2,3-butanedione monoxime (BDM)and 30 µM CPA did not further decrease delta mVO2. Although BDM (3-5 mM) decreased the delta mVO2 by 28-30% of control in a dose-independent manner, 3-5 mM BDM
decreased shortening in a dose-dependent manner. Our results indicate that the delta mVO2 of mouse LV slices during shortening under mechanically unloaded conditions consists of energy expenditure for total Ca2+ handling during excitation-contraction
coupling, basal metabolism, but no residual crossbridge cycling.
