J. Mchowat et al., SUBCELLULAR-DISTRIBUTION OF ENDOGENOUS LONG-CHAIN ACYLCARNITINES DURING HYPOXIA IN ADULT CANINE MYOCYTES, Cardiovascular Research, 27(7), 1993, pp. 1237-1243
Objective: Previous studies from our laboratory showed a pronounced in
crease in the sarcolemmal accumulation of long chain acylcarnitines in
isolated neonatal rat myocytes after a prolonged (60 minute) hypoxic
interval. Because much shorter intervals of hypoxia are associated wit
h electrophysiological alterations in adult cells, the present study w
as performed to assess the extent of sarcolemmal accumulation of long
chain acylcamitines during hypoxia in adult canine myocytes. Methods:
Cells were incubated (for 24 hours) with H-3-carnitine and the uniform
ity of incorporation into carnitine fractions was verified biochemical
ly. Cells were exposed to hypoxia (Po2<15 mm Hg) for 10 or 20 minutes
in the presence or absence of sodium -[5-(4-chlorophenyl)-pentyl]-oxir
ane-2-carboxylate (POCA; 10 muM), an inhibitor of carnitine acyltransf
erase I. Cells were processed for electron microscopical autoradiograp
hy with a technique to spatially fix endogenous long chain acylcamitin
es with selective and complete removal of short chain and free carniti
ne. Grain distributions were analysed by the maximum likelihood method
from digitised micrographs. Results: Total mass of long chain acylcam
itines increased ninefold [42.3(3.3) to 374(42) pmol.mg-1 protein] by
10 minutes of hypoxia and 15-fold [to 632(36) nmol.mg-1 protein] by 20
minutes of hypoxia. Normoxic cells exhibited little long chain acylca
rnitines in the sarcolemma, and modest amounts in mitochondria and cyt
oplasm. In hypoxic cells, content of long chain acylcarnitines in mito
chondria and cytoplasm increased by a maximum of twofold. By contrast,
long chain acylcarnitines increased 100-fold in the sarcolemma to 4.1
8 X 10(6) molecules.mum-3 after 10 minutes of hypoxia. The increase in
long chain acylcamitines with hypoxia was completely prevented by pre
treatment with POCA. Conclusion: Hypoxia in adult ventricular myocytes
induces a rapid and preferential increase in endogenous long chain ac
ylcamitines within the sarcolemma.