Effects of electrical stimulation and an intracellular calcium chelator on calcium movement in suspensions of isolated myocardial muscle cells.

The procedure of Haworth RA, Hunter DR and Berkoff HA (J Mol Cell Cardiol, 1980; 12:715-23) for the isolation of myocardial muscle cells from rat hearts has been modified by the addition of a step which involves centrifugation of the cells through a Percoll gradient. This increased the proportion of rod-shaped cells from 47 +/- 2.2 to 80 +/- 1.3% (mean +/- SEM, n = 7). In the absence of electrical stimulation but in the presence of 1.3 mmol . litre-1 Ca2+ less than 2% of the cells beat spontaneously. This number was not increased by addition of the Ca2+-selective ionophore A23187. A method in which isolated myocytes suspended in a cyclindrical incubation chamber are stimulated to beat by electrical impulses is described. At 1.3 mmol . litre-1 extracellular Ca2+, electrical stimulation increased by 30% the amount of 45Ca2+ exchanged in the period 0.25 to 3 min following addition of 45Ca2+. For myocytes subjected to electrical stimulation, the amount of 45Ca2+ exchanged increased as the concentration of extracellular Ca2+ increased. At 0.5 mmol . litre-1 extracellular Ca2+ verapamil reduced the amount of 45Ca2+ exchanged by 15% while La3+ reduced the amount of 45Ca2+ exchanged by 80%. Incubation of myocytes with the acetoxymethyl ester of the intracellular Ca2+ chelating agent bis (o-aminophenoxy)-ethane-N,N,N'N'-tetraacetic acid (BAPTA) for 45 min led to an inhibition of contraction.(ABSTRACT TRUNCATED AT 250 WORDS)