Fluctuations in the concentration of extracellular atp synchronized with intracellular ca2+ oscillatory rhythm in cultured cardiac myocytes

Isolated and cultured neonatal cardiac myocytcs contract spontaneously and cyclically. The intracellular concentration of free Ca2+ also changes rhythmically in association with the rhythmic contraction of myocytes (Ca2+ oscillation). Both the contraction and Ca2+ oscillatory rhythms are synchronized among myocytes, and intercellular communication via gap junctions has been considered primarily responsible for the synchronization. However, a recent study has demonstrated that intercellular communication via cxtracellular ATP-purinoceptor signaling is also involved in the intercellular synchronization of intracellular Ca2+ oscillation. In this study, we aim to elucidate whether the concentration of extracellular ATP changes cyclically and contributes to the intercellular synchronization of Ca2+ oscillation among myocytes. In almost all the cultured cardiac myocytes at four days in vitro (4 DIV), intracellular Ca2+ oscillations were synchronized with each other. The simultaneous measurement of the concentration of extracellular ATP and intracellular Ca2+ revealed the extracellular concentration of ATP actually oscillated concurrently with the intraccllular Ca2+ oscillation. In addition, power spectrum and cross-correlation analyses suggested that the treatment of cultured cardiac myocytes with suramin, a blocker of P2 purinoceptors, resulted in the asynchronization of Ca2+ oscillatory rhythms among cardiac myocytes. Treatment with suramin also resulted in a significant decrease in the amplitudes of the cyclic changes in both intracellular Ca2+ and extracellular ATP. Taken together, the present study demonstrated the possibility that the concentration of extracellular ATP changes cyclically in association with intracellular Ca2+, contributing to the intercellular synchronization of Ca2+ oscillation among cultured cardiac myocytes.