O2 consumption of mechanically unloaded contractions of mouse left ventricular myocardial slices.
Left ventricular (LV) myocardial slices were isolated from murine hearts (300 microm thick) and were stimulated at 1 Hz without external load. Mean myocardial slice O(2) consumption (MVo(2)) per minute (mMVo(2)) without stimulation was 0.97 +/- 0.14 ml O(2).min(-1).100 g LV(-1) and mean mMVo(2) with stimulation increased to 1.80 +/- 0.17 ml O(2).min(-1).100 g LV(-1) in normal Tyrode solution. Mean DeltamVo(2) (the mMVo(2) with stimulation - the mMVo(2) without stimulation) was 0.83 +/- 0.12 ml O(2).min(-1).100 g LV(-1). There were no differences between mean mMVo(2) with and without stimulation in Ca(2+)-free solution. The increases in extracellular Ca(2+) concentrations up to 14.4 mM did not affect the mMVo(2) without stimulation but significantly increased the mMVo(2) with stimulation up to 140% of control. The DeltamMVo(2) 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 microM) significantly reduced the DeltamMVo(2) to 0.27 +/- 0.06 ml O(2).min(-1).100 g LV(-1) (35% of control). The combination of 5 mM 2,3-butanedione monoxime (BDM) and 30 microM CPA did not further decrease DeltamMVo(2). Although BDM (3-5 mM) decreased the DeltamMVo(2) 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 DeltamMVo(2) of mouse LV slices during shortening under mechanically unloaded conditions consists of energy expenditure for total Ca(2+) handling during excitation-contraction coupling, basal metabolism, but no residual cross-bridge cycling.
Yamashita
Daisuke
D
Department of Physiology II, Nara Medical University, Kashihara 634-8521, Japan.
Kohzuki
Hisaharu
H
Kitagawa
Yutaka
Y
Nakashima
Tamiji
T
Kikuta
Akio
A
Takaki
Miyako
M
D000818:Animals; D002118:Calcium / Q000502:physiology; D003931:Diacetyl / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004734:Energy Metabolism; D005240:Feasibility Studies; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D010101:Oxygen Consumption / Q000187:drug effects; D016277:Ventricular Function, Left
D004338:Drug Combinations; D007211:Indoles; C004717:diacetylmonoxime; D003931:Diacetyl; D002118:Calcium; C000543:cyclopiazonic acid