The static preload associated myogenic spontaneous fasciculation response in lengthening cardiac muscle

Abstract

The passive tension force enhancement is one kind of myogenic spontaneous fasciculation in muscles. However, its physiological properties in cardiac fibres are not well known. In this study, mice cardiac papillary muscle spontaneous force enhancement was evaluated by micro stepping stretch method. The occurrence of spontaneous force and real time cardiac fibre Ca2+ redistribution was tranced by Flou-3 (2mM) indicator. Force enhancement amplitude, enhancement prolonging time, and tension–time integral were analysis by myograph analyser. The results indicated that the spontaneous force occurred immediately after the active stretch, rapidly enhanced during tolerating the sustained static stretch. The force occurrence and amplitude enhance synchronized with the Ca2+ recruitment and lightning transmitted to adjacent fibres. In high preload fibres, the enhancement was forceful to over its maximum passive tension (6.20 ± 0.51 N/mm2 to 4.49 ± 0.43 N/mm2). The force occurrences were unsteadiness in each stretch. The increased enhancement amplitude combining with the shortening prolonging time induced reduction of tension–time integral. We concluded that the intracellular Ca2+ synchronized force enhancement is one kind of interruption event in overloading cardiac fibres. This interruption occurred during the relaxation processing in cardiac muscle, therefore affect the rhythmic stability of cardiac relaxation-contraction cycle.