Arachidonic acid inhibits electrically induced intracellular calcium transients in neonatal rat cardiomyocytes

PROSTAGLANDINSLEUKOTRIENES ANDESSENTIALFATTYACIDS

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Arachidonic Acid Inhibits Electrically Induced Intracellular Transients in Neonatal Rat Cardiomyocytes P. Hoffmann,

D. Richards, P. Plews, I. Hoffmann-Heinroth,

I

Calcium

M. Toraason

Centerv_fbs Disease Control and PI-e\lention, National Imtitute for Occuputional Safety and Health. Cellular To.\-icohg! Section, 4676 Colwnhia Par-h?ay. Cincinnati. OH 45226, USA (Reprint requests to PHI .aBSTRACT. Calcium transients in single rat cardiomyocytes were inhibited in a concentration-dependent (25-100 PM) and reversible manner.

by arachidonic

acid (AA) exposure

INTRODUCTION

RESULTS

Arachidonic acid (AA) has recently been demonstrated to rapidly and reversibly block gap junctional intercellular communication in cardiomyocytes (1). This profound effect on a membrane transport process led us to examine the effects of AA on cytosolic free calcium concentration ([Ca’+]i) in cardiomyocytes during excitation-contraction coupling - a process dependent on membrane flux of Ca2+ and critically important for myocardial contraction and cardiac rhythm.

Addition of AA (25-100 PM) to cardiomyocytes caused a widening, a diastolic increase and a systolic decrease of electrically induced [Ca”], transients followed by a complete cessation of [Ca”], fluctuations (Figure). Average time to cessation of [Ca’+]; transients after exposure to 25, 50, and 100 PM AA was 14.5 f 3.3 min, 13.3 If: 10 min and 7.4 k 2.4 min (mean k- SD, n = 4-5). respectively. [Ca”], transients returned after washout of ,4A. These results demonstrate for the first time a concentration-dependent and reversible inhibition of Cal+ dynamics during excitation-contraction coupling by AA. It remains to be clarified, whether AA itself or its cyclooxygenase, lipoxygenase or cytochrome P-450 metabolites are responsible for the observed effects.

METHODS Preparation of neonatal rat ventricular myocytes and measurement of [Ca’+li in fura- loaded cells were performed as recently described (2). Myocytes were suffused with Hanks’ balanced salt solution (1.2 mM Ca?+) at 1 ml/min and paced at 1 Hz by field stimulation with two platinum electrodes at 60 V for 10 ms (Grass ,988 stimulator).

AND DISCUSSION

References Massey K, Minnich B N. Burt M. Arachidomc acid and llpoxygenaae metabolites uncouple neonatal rat cardiac myocyte pairs. Am .I Physiol 1992: 263: C-493. 2. Hoffmann P. Hoffmann-Heinroth I. Toraason M. Alterations by a thromboxanr A2 analogue ( LJ466 19I of calcium dynamics in isolated rat cardiomyocyte\. J Pharmacol Exper Ther 1993; 164: 336. I.

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Figure influence of 100 pM AA on electrically induced Ca transients in a single ventricular myocyte. A sequential series of three transients under steady-state conditions is shown. Transients were measured in the fura- loaded myocyte under control conditions followed by a IO-min exposure to 100 pM AA with a subsequent washout. A representative tracing of five experiments with 100 ktM AA is shown.