INCREASED LYSOPHOSPHATIDYLCHOLINE CONTENT INDUCED BY THROMBIN RECEPTOR STIMULATION IN ADULT-RABBIT CARDIAC VENTRICULAR MYOCYTES

Objective: The aims were (1) to determine whether thrombin, which is i ncreased in the presence of coronary thrombosis, can directly stimulat e the production of lysophosphatidylcholine, which has arrhythmogenic properties, in ventricular myocytes; (2) whether the effect is depende nt upon extracellular [Ca2+]; and (3) whether it is mediated directly through stimulation of the thrombin receptor. Methods: Lipids were ext racted from isolated adult rabbit ventricular myocytes and lysophospha tidylcholine was isolated by HPLC and quantified using a recently deve loped radiometric assay employing H-3-acetic anhydride. Results: Throm bin (0.05 U.ml(-1)) of ventricular myocytes resulted in a nearly sixfo ld increase in lysophosphatidylcholine levels [0.26(SEM 0.03) to 1.61( 0.42) nmol.mg(-1) protein] within 1 min. The increase in myocytic lyso phosphatidylcholine content was prevented by preincubation of thrombin with the proteolytic site inhibitors phenylyl-prolyl-arginyl-chlorome thyl ketone (PPACK) and dansylarginine N-(3-ethyl-1,5-pentanediyl)amid e. The increase in lysophosphatidylcholine content in response to thro mbin was not present at an extracellular calcium concentration ([Ca2+] (0)) = 500 mu M, but was marked at a physiological level of [Ca2+](0) = 1.8 mM. Stimulation of myocytes with the thrombin receptor activatin g peptide SFLLRNPNDKYEPF (100 mu M for 1 min) resulted in a similar in crease in lysophosphatidylcholine content [1.61(0.27) nmol.mg(-1) prot ein]. Conclusions: The marked increase in lysophosphatidylcholine cont ent in cardiac myocytes in response to thrombin has important implicat ions as an arrhythmogenic mechanism during early myocardial ischaemia.