AJP - Cell Physiology, Vol 253, Issue 6 C846-C853, Copyright © 1987 by American Physiological Society
Biochemical and subcellular distribution of arachidonic acid in rat myocardium
Y. Miyazaki, R. W. Gross, B. E. Sobel and J. E. Saffitz
Cardiovascular Division, Washington University, St. Louis, Missouri 63110.
Selective release of arachidonic acid from prelabeled phospholipid pools
has been observed following exposure of neonatal rat cardiac myocytes to
metabolic inhibitors in vitro and has been correlated temporally with the
development of irreversible sarcolemmal damage. Hydrolysis of phospholipids
with release of arachidonic acid may be an important mechanism in the
pathogenesis of sarcolemmal damage induced by ischemia. To elucidate
potential subcellular loci of arachidonic acid release in ischemic
myocardium, we characterized the phospholipid composition of adult rat
myocardial sarcolemma and delineated the biochemical and subcellular
distribution of radiolabeled arachidonic acid in neonatal rat myocytes
incubated with [3H]-arachidonic acid for selected intervals. Although
arachidonic acid comprised 13 +/- 3% of total aliphatic moieties in
combined choline and ethanolamine glycerophospholipids isolated from
purified adult rat myocardial sarcolemma, radiolabeled arachidonic acid
could not be detected in sarcolemma of cultured neonatal rat myocytes
incubated with 5 nM [3H]arachidonic acid for 24 h. Radioactivity was
located almost exclusively in mitochondria and internal cytoplasmic
membranes (primarily sarcoplasmic reticulum), which collectively contained
90% of myocyte radioactivity. These results indicate that radiolabeled
arachidonic acid released from prelabeled phospholipid pools on exposure of
neonatal rat myocytes to oxidative inhibitors is derived from mitochondria
and internal cell membranes. The diminutive labeling of the sarcolemma
suggests that turnover of arachidonoyl phospholipids is slower in the
sarcolemma than in other membranous organelles.
