Twitch energetics in mouse papillary muscle were consistent with ATP splitting by half the cross-bridges and pumping of one Ca2+ into the sarcoplasmic reticulum for every three cross-bridge cycles.
The energetics of a cardiac twitch in mouse papillary muscle are consistent with half the cross-bridges completing one ATP-splitting cycle per twitch, independent of shortening velocity.
The aim of this study was to quantify the fraction of cross-bridges that cycle during a cardiac twitch. Measurements of the energetics of contracting left ventricular mouse papillary muscle were made in vitro (27 degrees C) using the myothermic technique. Enthalpy output was partitioned into force-dependent and force-independent components using 2,3-butanedione monoxime (BDM) to selectively inhibit cross-bridge cycling. For isometric contractions and a contraction frequency of 2 Hz the net enthalpy output was 5.7 +/- 0.8 mJ g(-1) twitch(-1) and initial enthalpy output was 2.3 +/- 0.3 mJ g(-1) twitch(-1) (n = 11). Assuming that low concentrations of BDM did not affect Ca2+ cycling, force-independent enthalpy output was 18.6 +/- 1.9% (n = 7) of the initial enthalpy output. Enthalpy output decreased with increased contraction frequency but was independent of shortening velocity. On the basis of these values, it was calculated that the twitch energetics were consistent with ATP splitting by half the cross-bridges and the pumping of one Ca2+ into the sarcoplasmic reticulum for every three cross-bridge cycles. The simplest interpretation is that half the cross-bridges completed one ATP-splitting cycle in each twitch. The lack of influence of shortening velocity on energy cost supports the idea that the amount of energy to be used is determined early in a twitch and is not greatly influenced by events that occur during the contraction.
Widén et al. (Fri,) conducted a other in Left ventricular mouse papillary muscle (n=11). 2,3-butanedione monoxime (BDM) was evaluated on Enthalpy output and fraction of cross-bridges cycling. Twitch energetics in mouse papillary muscle were consistent with ATP splitting by half the cross-bridges and pumping of one Ca2+ into the sarcoplasmic reticulum for every three cross-bridge cycles.