Studies on heat. XVII. Effects of frog heart inotropic substances on beating of rat myocardial cells in culture.

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Abstract
The effects of frog heart inotropic substances on beating phenomena in cultured myocardial cells of neonatal rats were investigated. The beating rate and percentage of trypsin-dissociated cells were determined in Eagle minimum essential medium (MEM) supplemented with 10% bovine serum at 2 days in culture. The attachment and the spreading of cells were observed in Eagle MEM supplemented with 0.5% bovine albumin. The positive inotropic glycoprotein, Fr. A from calf heart, and its cyanogen bromide peptide, Fr. A-1, significantly increased the beating rate and percentage of single cells in their dosages to be effective on frog heart assay and epinephrine. Another positive inotropic lipoprotein, Fr. I-B from calf thymus, also increased the rate but did not affect the percentage like acetylcholine. The negative inotropic dipeptide, anserine, decreased the rate but not the percentage of single cells. In the beating rate of cell-cluster, Fr. A, Fr. A-1 and Fr. I-B showed accelerating effects in their concentrations of 10-8 M, 10-7 M and 10-9 M, respectively. The effect of Fr. I-B on cell-cluster was transitory 5-20 min after sample addition, and those of Fr. A and Fr. A-1 were relatively continuous up to 40 min. The chronotropic actions on cell-cluster by these 3 samples were not affected by the addition of propranolol. Fr. A significantly increased the attached cells and Fr. I-B greatly decreased the spreading cells, but neither the promoted the spreading process of myocardial cells at doses that improved the beating properties.