ARACHIDONIC-ACID DISRUPTS CALCIUM DYNAMICS IN NEONATAL RAT CARDIAC MYOCYTES

Objectives: The purpose of this study was to investigate the effects o f prolonged arachidonic acid (AA) exposure on electrically induced flu ctuations of cytosolic free Ca2+ concentration ([Ca2+](i)) in cardiac myocytes and to identify intracellular biochemical events that may pla y a role in the actions of AA on [Ca2+](i) dynamics. Methods: Electric ally induced [Ca2+](i) transients were investigated in cultured single neonatal rat ventricular myocytes using spectrofluorometric analysis of fura-2-[Ca2+](i) binding. KCl-induced depolarization, caffeine and ryanodine were used to assess the effects of AA on Ca2+ handling by th e sarcolemma and the sarcoplasmic reticulum. Prostanoid formation was measured with an ELISA technique. alpha-Tocopherol was used to determi ne if free radical formation was a factor in the AA effects on [Ca2+]( i). Results: Exposure to 10-30 mu M AA produced a concentration-depend ent and reversible configuration change and eventually a cessation of [Ca2+](i) transients. Continued exposure resulted in a Ca2+ overload(t onic [Ca2+](i) greater than peak systolic [Ca2+](i)). AA did not influ ence KCl-induced [Ca2+](i) increase but did eliminate caffeine-induced [Ca2+](i) transients. AA exposure stimulated the formation of 6-oxo-p rostaglandin F-1 alpha in a concentration-dependent manner, but thromb oxane B-2 formation was not influenced. alpha-Tocopherol pretreatment significantly delayed times till cessation of [Ca2+](i) transients and Ca2+ overload, whereas ryanodine and cyclo-oxygenase inhibitors were without effect. Conclusions: The present data provide evidence that th e initial action of AA on [Ca2+](i) transients during excitation-contr action coupling involves an effect of AA on sarcolemmal Ca2+ influx an d sarcoplasmic reticulum Ca2+ handling. AA-induced cessation of electr ically induced [Ca2+](i) transients and Ca2+ overload may involve the formation of free radicals.