LYSOPHOSPHATIDYLCHOLINE-INDUCED CA2+-OVERLOAD IN ISOLATED CARDIOMYOCYTES AND EFFECT OF CYTOPROTECTIVE DRUGS

It has been previously demonstrated that lysophosphatides accumulate rapidly in ischaemic tissue, and may play a key role in the genesis of ischaemia-reperfusion injury. The present study investigated the effects of exogenously added lysophosphatidylcholine (1-20 μm) on single isolated cardiomyocytes from adult rabbit hearts. Quiescent cells exposed to ≥8 μm lysophosphatidylcholine dose-dependently displayed irreversible hypercontraction, whereas after 60 min at 3 μm lysophosphatidylcholine, most cells remained rod-shaped (87.2 ± 2.0%, mean ± s.e.m.). However, when combined with electrical field stimulation (1 Hz), exposure to 3 μm lysophosphatidylcholine resulted in irreversible hypercontracture of most cells after 60 min: only 27.5 ± 7.5% of the cells remained rod-shaped. Contracture depended upon the presence of extracellular Ca2+, and coincided with a significant rise in the median intracellular free Ca2+ level from 72.2 to 352.1 nm (P = 0.0001), suggesting intracellular Ca2+-overload. Pretreatment with 10-6m flunarizine or R 56865 significantly reduced the fraction of damaged cells when exposed to 3 μm lysophosphatidylcholine and electrical stimulation: 78.3 ± 12.2% and 56.3 ± 13.1% respectively of the cells remained rod-shaped. No protection was observed when quiescent cells were exposed to 10 μm lysophosphatidylcholine. Cytochemical localization of Ca2+ showed that lysophosphatidylcholine induced a loss of sarcolemma-bound Ca2+ precipitate and an accumulation of Ca2+ clusters in mitochondria of damaged cells in a dose and time dependent way. These results suggest that lysophosphatidylcholine induces functional and structural damage (Ca2+-overload) in isolated cardiomyocytes and that this can be prevented by cytoprotective drugs. © 1992.