Exogenous phospholipase enzymes mimic effects of phenylephrine on Ca2+ transport in hepatocytes

Phospholipase C from Clostridium perfringens induced the release of 45Ca2+ from isolated rat hepatocytes incubated at 0.1 mM extracellular Ca2+ with a time course similar to that for the action of phenylephrine. Under the conditions of these experiments, no significant damage to the plasma membrane was detected in the presence of phospholipase C. Little 45Ca2+ release was induced by bee venom phospholipase A2. At 1.3 mM extracellular Ca2+, both phospholipase enzymes stimulated the initial rate of 45Ca2+ exchange. Concentrations of phospholipase C comparable with those that stimulated 45Ca2+ release increased the rates of glucose release and O2 utilization by 70 and 20% respectively. An increase in the rate of O2 utilization but not glucose release was observed after the addition of phospholipase A2 to hepatocytes. The possible role for a cellular phospholipase C in the mechanism by which phenylephrine stimulates glycogenolysis in the liver cell is briefly discussed.