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-opioid receptor stimulation in the heart of
chronically hypoxic rats
Department of Physiology and Institute of Cardiovascular Sciences and Medicine, Faculty of Medicine, The University of Hong Kong, Hong Kong, China
-Opioid receptor (
-OR)
stimulation with U50,488H, a selective
-OR agonist, or activation of
protein kinase C (PKC) with 4-phorbol 12-myristate 13-acetate (PMA), an
activator of PKC, decreased the electrically induced intracellular
Ca2+ ([Ca2+]i) transient and
increased the intracellular pH (pHi) in single ventricular
myocytes of rats subjected to 10% oxygen for 4 wk. The effects of
U50,488H were abolished by nor-binaltorphimine, a selective
-OR
antagonist, and calphostin C, a specific inhibitor of PKC, while the
effects of PMA were abolished by calphostin C and
ethylisopropylamiloride (EIPA), a potent Na+/H+
exchange blocker. In both right hypertrophied and left
nonhypertrophied ventricles of chronically hypoxic rats, the effects of
U50,488H or PMA on [Ca2+]i transient and
pHi were significantly attenuated and completely abolished,
respectively. Results are first evidence that the
[Ca2+]i and pHi responses to
-OR stimulation are attenuated in the chronically hypoxic rat heart,
which may be due to reduced responses to PKC activation. Responses to
all treatments were the same for right and left ventricles, indicating
that the functional impairment is independent of hypertrophy.
-OR
mRNA expression was the same in right and left ventricles of both
normoxic and hypoxic rats, indicating no regional specificity.
hypoxia; hypertrophy; protein kinase C; intracellular calcium; intracellular pH; heart
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