Effects of basal [Ca2+](i) on calcium handling in Ca2+-overloaded rat cultured heart muscle cells

To elucidate the relationship between intracellular free Ca2+ concentration ([Ca2+](i)) and Ca2+ signalling by the sarcoplasmic reticulum (SR) in Ca2+-overloaded heart muscle cells, the direct effects of ''basal'' [Ca2+](i), on calcium waves were investigated by altering the membrane potential. When basal inter-calcium wave (BCW) [Ca2+](i) was maintained at a high level, (i) calcium waves showed more gradual and more rapidly sup pressed increase in [Ca2+]-profile (P < 0.005), and (ii) calcium waves occurred at a significantly higher frequency and velocity (259% and 137%), than when low BCW [Ca2+](i) was maintained. Similar investigations on inhibition of the Na+-Ca2+ exchanger, however, showed that membrane potential did not elicit direct effects on calcium waves. These results shelved that the elevation of BCW [Ca2+](i) per se directly influences Ca2+-signalling in heart muscle cells through non-equilibrated release-restoration Ca2+-handling by the SR. (C) 1997 Elsevier Science Inc.