Calcium metabolism in rat hepatocytes

Abstract

The total Ca concentration in rat hepatocytes was 7.9 .mu.g-atoms/g dry wt; 77% of this was mitochondrial. Approximately 20% of cell Ca exchanged with 45Ca within 2 min. Thereafter incorporation proceeded at a low rate to reach 28% of total Ca after 60 min. Incorporation into mitochondria showed a similar time course and accounted for 20% of mitochondrial total Ca after 60 min. The .alpha.-adrenergic agonists phenylephrine and adrenaline [epinephrine] + propranolol stimulated incorporation of 45Ca into hepatocytes. Phenylephrine was shown to increase total Ca in hepatocytes. Phenylephrine inhibited efflux of 45Ca from hepatocytes perifused with Ca-free medium. Glucagon, dibutyryl cyclic[c]AMP and .beta.-adrenergic agonists adrenaline and 3-isobutyl-1-methylxanthine stimulated Ca efflux from hepatocytes perifused with Ca-free medium. The effect of glucagon was blocked by insulin. Insulin itself had no effect on Ca efflux and it did not affect the response to dibutyryl cAMP. Incorporation of 45Ca into mitochondria in hepatocytes was stimulated by phenylephrine and inhibited by glucagon and by carbonyl cyanide p-trifluoromethoxyphenylhydrazone. The effect of glucagon was blocked by insulin. Ionophore A23187 stimulated hepatocyte uptake of 45Ca, uptake of 45Ca into mitochondria in hepatocytes and efflux of 45Ca into a Ca-free medium.