Spontaneous activity of rat embryonic cardiac myocytes

Abstract

Rat embryonic cardiac myocytes display a spontaneous activity, which manifests itself as a repetitive change in a number of cellular properties, resulting in an oscillatory contractile behavior with a beating frequency of about 1 Hz. Fluo-4 loaded cardiac cells in primary culture demonstrated large fluctuating increases of the intracellular free calcium concentration. Long-term recordings of extracellular field potentials with microelectrode arrays from 60 planar electrodes showed repetitive electrical membrane depolarizations that coincided with the whole-cell Ca2+ transients. Whole-cell patch clamp analysis revealed the existence of regular membrane depolarizations. A close correlation between the three processes was noticed. Such a correlation was confirmed in the absence of extracellular calcium, which reversibly halted the appearance of the whole-cell Ca2+ transients and the electrical processes. Involvement of membrane depolarizations was suggested, because cellular depolarization prevented the spontaneous activity of the cardiomyocytes. In conclusion, our experiments suggest that the oscillations in intracellular calcium and the membrane depolarizations that we observe in rat embryonic cardiac myocytes reflect Ca2+ influx after membrane depolarization. The processes responsible for the membrane depolarizations remain to be elucidated. © 2009 Springer-Verlag.