Fluctuations in the concentration of extracellular ATP synchronized with intracellular Ca(2+) oscillatory rhythm in cultured cardiac myocytes

Abstract

Isolated and cultured neonatal cardiac myocytes contract spontaneously and cyclically. The intracellular concentration of free Ca(2+) also changes rhythmically in association with the rhythmic contraction of myocytes (Ca(2+) oscillation). Both the contraction and Ca(2+) 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 extracellular ATP-purinoceptor signaling is also involved in the intercellular synchronization of intracellular Ca(2+) oscillation. In this study, we aim to elucidate whether the concentration of extracellular ATP changes cyclically and contributes to the intercellular synchronization of Ca(2+) oscillation among myocytes. In almost all the cultured cardiac myocytes at four days in vitro (4 DIV), intracellular Ca(2+) oscillations were synchronized with each other. The simultaneous measurement of the concentration of extracellular ATP and intracellular Ca(2+) revealed the extracellular concentration of ATP actually oscillated concurrently with the intracellular Ca(2+) 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 Ca(2+) oscillatory rhythms among cardiac myocytes. Treatment with suramin also resulted in a significant decrease in the amplitudes of the cyclic changes in both intracellular Ca(2+) and extracellular ATP. Taken together, the present study demonstrated the possibility that the concentration of extracellular ATP changes cyclically in association with intracellular Ca(2+), contributing to the intercellular synchronization of Ca(2+) oscillation among cultured cardiac myocytes.