Sarcomere length does not modulate cross-bridge turnover rates (k(tr)) in human, murine, and porcine permeabilized cardiomyocytes, despite significant species differences in k(tr) magnitude.
Species differences exert a major influence on the rate of tension redevelopment, but sarcomere length does not modulate cross-bridge turnover rates in human, murine, and porcine hearts.
The increase in Ca(2+) sensitivity of isometric force development along with sarcomere length (SL) is considered as the basis of the Frank-Starling law of the heart, possibly involving the regulation of cross-bridge turnover kinetics. Therefore, the Ca(2+) dependencies of isometric force production and of the cross-bridge-sensitive rate constant of force redevelopment (k(tr)) were determined at different SLs (1.9 and 2.3 mum) in isolated human, murine, and porcine permeabilized cardiomyocytes. k(tr) was also determined in the presence of 10 mM inorganic phosphate (P(i)), which interfered with the force-generating cross-bridge transitions. The increases in Ca(2+) sensitivities of force with SL were very similar in human, murine, and porcine cardiomyocytes (DeltapCa(50): approximately 0.11). k(tr) was higher (P < 0.05) in mice than in humans or pigs at all Ca(2+) concentrations (Ca(2+)) maximum k(tr) (k(tr,max)) at a SL of 1.9 mum and pCa 4.75: 1.33 +/- 0.11, 7.44 +/- 0.15, and 1.02 +/- 0.05 s(-1), in humans, mice, and pigs, respectively but k(tr) did not depend on SL in any species. Moreover, when the k(tr) values for each species were expressed relative to their respective maxima, similar Ca(2+) dependencies were obtained. Ten millimolar P(i) decreased force to approximately 60-65% and left DeltapCa(50) unaltered in all three species. P(i) increased k(tr,max) by a factor of approximately 1.6 in humans and pigs and by a factor of approximately 3 in mice, independent of SL. In conclusion, species differences exert a major influence on k(tr), but SL does not appear to modulate the cross-bridge turnover rates in human, murine, and porcine hearts.
Édes et al. (Fri,) conducted a other in Cardiomyocyte physiology. Sarcomere length variation (1.9 and 2.3 μm) and inorganic phosphate (10 mM) was evaluated on Ca(2+) dependencies of isometric force production and rate constant of force redevelopment (k(tr)). Sarcomere length does not modulate cross-bridge turnover rates (k(tr)) in human, murine, and porcine permeabilized cardiomyocytes, despite significant species differences in k(tr) magnitude.