PHOSPHATIDYLCHOLINE METABOLISM IN HYPOXIC AND PHOSPHOLIPASE-C EXPOSEDRAT VENTRICULAR MYOCYTES

A phospholipase C specific for choline and ethanolamine acyl and plasm alogen glycerophospholipids (PC-PLC) has been described in myocardial tissue. In the present study we investigated whether an endogenous PC PLC is activated in hypoxic, substrate-free incubations of rat ventric ular myocytes. The phosphatidylcholine pool of the myocytes was prelab elled with [C-14]choline during a 4-h preincubation (pulse) period. Th e myocytes were subsequently washed and incubated for another 2 h (cha se period) in normoxic, hypoxic, or hypoxic buffer supplemented with P C-PLC from Bacillus cereus. We hypothesized that an increase in the to tal (intracellular plus extracellular) content of [C-14]phosphocholine (one of the products resulting from PC-PLC action on phosphatidylchol ine) throughout the chase period would indicate PC-PLC activity. Inste ad, an apparent decrease was observed for this parameter in all myocyt e groups (17-29%), even in the one exposed to exogenous PC-PLC. Howeve r, 60 min after the start of the chase period, the level of total [C-1 4]phosphocholine was higher in hypoxic (p = 0.022) and hypoxic + PC-PL C exposed (p = 0.013) myocytes compared with normoxic controls. The to tal content of [C-14]choline increased significantly (p < 0.017) in al l myocyte groups during the incubation period (98-153%) as a result of an increment of this metabolite in the buffer. Furthermore, the value s measured in hypoxic and hypoxic + PC-PLC exposed myocytes during the first hour of the chase period were significantly (p < 0.017) higher than the corresponding values in normoxic myocytes. The present result s do not allow firm conclusions regarding endogenous PC-PLC activation in energy-depleted rat cardiac myocytes. On the other hand, the data suggest activation of phosphocholine phosphatase or phospholipase D un der these conditions.