Measurement of cytosolic calcium with aequorin in dispersed rat ventricular cells.

The changes in the cytosolic concentration of free calcium of adult rat cardomyocytes were monitored using aequorin incorporated by hypoosmotic shock. The majority of the myocytes retained their rod-like appearance and their tolerance to a normal concentration of extracellular calcium. The aequorin signal was increased by depolarization, by an increase in extracellular calcium, by substitution of extracellular sodium with either choline or tetramethylammonium, by 20 mM NH4Cl or by hypoxia. In these myocytes, isoproterenol or the phosphodiesterase inhibitor MIX (3-isobutyl-l-methylxanthine) enhanced the ability of the cells to buffer calcium loads while the mitochondrial inhibitor FCCP (carbonyl cyanide p-trifluoromethoxy-phenyl-hydrazone), decreased their calcium buffering capacity.