It has been shown that incorporation of slow skeletal troponin I (ssTnI) into the cardiac sarcomere is associated with enhancement of myofilament Ca2+ sensitivity; it has also been suggested that ssTnI may affect cross-bridge cycle kinetics (Kentish et al. Circ. Res. 88, 1059-1065, 2001). The present study was aimed to 1) test the hypothesis that ssTnI is sufficient to impart increased Ca2+ sensitivity in any striated muscle, and 2) to directly determine the impact of ssTnI on cross-bridge kinetics by means of rabbit psoas single myofibrils activated and relaxed by rapid solution switching. Myofibril native fast skeletal Tn (control) was replaced by recombinant whole cardiac Tn (cTn), or a Tn chimera composed of cTnC, cTnT, and ssTnI. The replacement was confirmed by SDS gel analysis. Myofibril steady state force-[Ca2+] relations were fit to the Hill equation yielding maximum force (P0), calcium sensitivity (EC50), and cooperativity (nH). P0 was not different among myofibril groups, while introduction of either cTn or the ssTnI chimera resulted in a significant decrease in nH. cTn induced a marked decrease in EC50; the presence of ssTnI further decreased EC50. Despite the marked impact of either cTn or the ssTnI chimera on Ca2+ sensitivity, we found no effect on either the rate of force development upon Ca2+ activation, the rate of force redevelopment following a quick release-restretch, or force relaxation kinetics upon rapid Ca2+ removal. Our data suggest that 1) the presence of ssTnI is sufficient to impart increased myofilament calcium sensitivity in any striated muscle type, 2) the Tn composition and related alterations in thin filament activation dynamics does not affect the intrinsic cross-bridge cycle kinetics
Troponin composition affects myofilament sensitivity but no cross-bridges cycle kinetics / Scellini B.; Belus A.; Piroddi N.; Tesi C.; Poggesi C.. - In: BASIC AND APPLIED MYOLOGY. - ISSN 1120-9992. - STAMPA. - 15(3&4):(2005), pp. 164-165.
Troponin composition affects myofilament sensitivity but no cross-bridges cycle kinetics.
SCELLINI, BEATRICE;BELUS, ALEXANDRA ANNA SOPHIE;PIRODDI, NICOLETTA;TESI, CHIARA;Poggesi C.
2005
Abstract
It has been shown that incorporation of slow skeletal troponin I (ssTnI) into the cardiac sarcomere is associated with enhancement of myofilament Ca2+ sensitivity; it has also been suggested that ssTnI may affect cross-bridge cycle kinetics (Kentish et al. Circ. Res. 88, 1059-1065, 2001). The present study was aimed to 1) test the hypothesis that ssTnI is sufficient to impart increased Ca2+ sensitivity in any striated muscle, and 2) to directly determine the impact of ssTnI on cross-bridge kinetics by means of rabbit psoas single myofibrils activated and relaxed by rapid solution switching. Myofibril native fast skeletal Tn (control) was replaced by recombinant whole cardiac Tn (cTn), or a Tn chimera composed of cTnC, cTnT, and ssTnI. The replacement was confirmed by SDS gel analysis. Myofibril steady state force-[Ca2+] relations were fit to the Hill equation yielding maximum force (P0), calcium sensitivity (EC50), and cooperativity (nH). P0 was not different among myofibril groups, while introduction of either cTn or the ssTnI chimera resulted in a significant decrease in nH. cTn induced a marked decrease in EC50; the presence of ssTnI further decreased EC50. Despite the marked impact of either cTn or the ssTnI chimera on Ca2+ sensitivity, we found no effect on either the rate of force development upon Ca2+ activation, the rate of force redevelopment following a quick release-restretch, or force relaxation kinetics upon rapid Ca2+ removal. Our data suggest that 1) the presence of ssTnI is sufficient to impart increased myofilament calcium sensitivity in any striated muscle type, 2) the Tn composition and related alterations in thin filament activation dynamics does not affect the intrinsic cross-bridge cycle kinetics
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