Positive inotropism in hypothermia partially depends on an increase in maximal Ca(2+)-activated force.
We investigated the contribution of maximal Ca(2+)-activated force to the positive inotropism induced by mild hypothermia. Phosphorus-31 nuclear magnetic resonance spectroscopy revealed that neither energy-related phosphorus compounds in myocardium nor intracellular pH was responsible for the change in contractility. Maximal Ca(2+)-activated pressure (MCAP), the intact-heart correlate of maximal Ca(2+)-activated force, was determined in isolated perfused rabbit hearts by measuring isovolumic left ventricular pressure during tetani at extracellular Ca2+ concentrations greater than or equal to 10 mM. Tetani were elicited by rapid pacing after exposure to ryanodine. MCAP increased by 2.17 +/- 0.28% (mean +/- SE, P less than 0.001, n = 19) for each degree of myocardial cooling between 30 and 38 degrees C. Our results indicate that a primary change in myofilament Ca2+ responsiveness underlies the positive inotropism in hypothermia. The increase in maximal Ca(2+)-activated force may explain the observation of positive inotropism without an upward shift in the relation between oxygen consumption and pressure-volume area, as previously reported for cooled whole hearts.
First Department of Medicine, Osaka University Medical School, Fukushima, Osaka.
H
H
Kusuoka
Y
Y
Ikoma
S
S
Futaki
H
H
Suga
A
A
Kitabatake
T
T
Kamada
M
M
Inoue
D000818:Animals; D002118:Calcium / Q000502:physiology*; D004734:Energy Metabolism; D006321:Heart / Q000503:physiopathology; D007035:Hypothermia / Q000378:metabolism / Q000503:physiopathology*; D066298:In Vitro Techniques; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism; D011312:Pressure; D011817:Rabbits
D010758:Phosphorus; D002118:Calcium