Rhythmic contraction and intracellular Ca2 + oscillatory rhythm in spontaneously beating cultured cardiac myocytes

Cultured cardiac myocytes from neonatal rats show spontaneous and rhythmic contractions. The intracellular concentration of free Ca^2?+? also changes rhythmically, associated with the rhythmic contraction of myocytes (Ca^2?+? oscillation). This study aims to elucidate whether spontaneous rhythmic contraction affects the dynamics of intracellular Ca^2?+? oscillation in cultured cardiac myocytes. In cultures at four days in vitro (4 DIV), spontaneous Ca^2?+? oscillation was synchronized among myocytes. Treatment of cultures with an uncoupler of E?-?C coupling resulted in a cessation of the spontaneous contraction of cardiac myocytes, but did not abolish the Ca^2?+? oscillation. The intercellular synchronization of intracellular Ca^2?+? oscillation persisted, and both the intervals and the fluctuation of the oscillation tended to increase after the termination of rhythmic contraction. The present study demonstrated that mechanical factors associated with rhythmic contraction did not affect the intercellular synchronization of intracellular Ca^2?+? oscillation, but possibly contributed to the stability of the oscillatory rhythm.