EFFECTS OF HYPOTHERMIA AND REWARMING ON PHOSPHOLIPASE-C-EVOKED GLYCEROL OUTPUT IN RAT MYOCARDIAL-CELLS

The combined action of phosphatidylcholine preferring phospholipase C (PC-PLC) and intracellular lipases has recently been shown to cause glycerol output in energy deprived rat cardiomyocytes. In the present study we examined the effect of hypothermia and rewarming on PC-PLC evoked glycerol output in freshly isolated, calcium-tolerant myocytes. The cells were preincubated for 60 min at hypothermic (5°C) or normothermic (37°C) conditions in Krebs-Henseleit bicarbonate buffer (pH 7.4) supplemented with 1 mm DL-carnitine, 1% B.S.A. and 5 mm glucose. Addition of PC-PLC resulted in a significantly higher (P<0.05) output of glycerol in myocytes undergoing rewarming than in myocytes kept constantly at 5°C or 37°C. The values obtained for PC-PLC induced glycerol output (difference in glycerol output between incubations with and without PC-PLC) were 6.77 ± 2.6 (37°C), 4.54 ± 1.7 (5°C) and 22.85 ± 5.9 (5-37°C) nmol 106 cells ·h. Rewarming in addition caused a significantly higher (P<0.05) leakage of lactate dehydrogenase (LDH) from the rewarmed cells as compared to cells at constant temperatures (5°C or 37°C). However, there was no additional effect of PC-PLC on LDH leakage. The elevated PC-PLC induced glycerol output in rewarmed myocytes was not related to a fall in the percentage of rod-shaped cells or a reduced cellular content of ATP, since no differences could be detected between the various myocyte preparations with respect to these parameters. These data instead suggest that hypothermic events may cause discreet structural derangements in the phospholipid bilayer of the sarcolemma which will favour PC-PLC attack in the subsequent rewarming phase. © 1992.