Developed tension (T), its maximal rate of rise [+dT/dt(max)], and maximal velocity of relaxation [-dT/dt(max)] were measured in cat papillary muscles, after changes in calcium concentration (Ca2+) at pH ~7.0, 7.4, and 7.6, produced by altering the PCO2 of the medium. Only the results obtained at the two extreme pH values were compared. Increasing [Ca2+] increased T, +dT/dt(max) and -dT/dt(max). At a given [Ca2+] high PCO2 significantly decreased T and +dT/dt(max). When T and +dT/dt(max) vs. [Ca2+] were plotted reciprocally, the ordinate intercepts of the lines, 1/E(max) significantly increased in acidosis (P <0.01). These data do not support the view of a competitive action between H+ and Ca2+ ions on the mechanical behavior of cardiac muscle. At a given [Ca2+], +dT/dt(max) was depressed significantly more than -dT/dt(max), i.e., at a [Ca2+] of 10 mM, the degree of depression of +dT/dt(max) and -dT/dt(max) was 41 ± 4% and 23 ± 5%, respectively (P <0.01). Furthermore, the slope of the regression line -dT/dt(max) vs. +dT/dt(max) was significantly higher in acidosis (P <0.01). Similar results were obtained in muscles depleted of catecholamines. These findings suggest that H+ ion might act upon the relaxation process.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|State||Published - 1979|
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