Effect of Change in Growth Environment on Cultured Myocardial Cells Investigated in a Standardized Medium

Neonatal rat heart cells cultivated in either of two different media which varied only in their serum supplements were transferred to chemically defined medium (Ham's F10) for 24 h before measuring a variety of parameters. The 24-h period of exposure to chemically defined medium was not sufficient to reverse the effects imposed on the cells by the serum used in the first phase of growth. The cells differed in rate and duration of action potentials and contractions. The initial serum composition affected the response of the cells to calcium deficiency. Studies involving the effects of pharmaceutical reagents such as isoproterenol were also influenced by the serum. In attempting to determine the cause and possible mechanism, it was found that mitochondrial membrane permeability for nitroblue tetrazolium (NBT) was unchanged. Although the serum supplements differed in fatty acid composition, the fatty acid profiles of the cell phospholipids were relatively constant. We conclude that (a) the function of the cells is affected by the growth environment, particularly serum; (b) that a short exposure to a uniform chemically defined medium is not sufficient to reverse these effects; and (c) that the differences in effects are not the result of changes in the fatty acid composition of the whole cell phospholipids nor in mitochondrial membrane permeability as measured by NBT.