k-Opioid Receptor Dependent Cardioprotection in the Rat
Activation of opioid receptors dramatically decreases the degree of ischemic damage in rat myocardium. This cardioprotective phenomenon may be mediated by a protein kinase C (PKC)-dependent modification of myofibrillar proteins, leading to reduced ATP utilization by the myofilaments. We tested this hypothesis by correlating post-ischemic contractile recovery and myofibrillar actomyosin Mg2+ATPase activity in isolated rat hearts. Pre-ischemic treatment with the k-opioid receptor agonist U50,488 (U50, 1 mM) improved post-ischemic left ventricular developed pressure (LVDP) by 35% over control hearts. Non-ischemic and post-ischemic myofibrillar actomyosin Mg2+ATPase activity were reduced by 20% in U50 treated hearts, as compared to control hearts. Decreased myofilament ATP consumption with cardioprotective agents was also demonstrated in isolated ventricular myocytes. The PKC-activator phorbol 12-myristate acid (1 mM) and U50 both slowed the maximal velocity of unloaded shortening by 15% to 25%. Exogenous PKC-e mimicked the U50-dependent reduction in myofibrillar actomyosin Mg2+ATPase activity. ATP levels were 173% higher in non-ischemic hearts treated with U50, and 107% higher at the end of ischemia, compared to control hearts, which is consistent with decreased ATP utilization by the myofilaments. The improved post-ischemic LVDP and U50-dependent decrease in actomyosin Mg2+ATPase activity were blocked by the PKC inhibitors chelerythrine chloride (2 mM) and bisindolylmaleimide (100 nm). Confocal microscopy and Western blot analysis of isolated ventricular myocytes showed translocation of PKC-e and -d to the myofibrillar fraction with U50 treatment. U50 increased myofibrillar Ca2+-independent PKC activity. U50 treatment resulted in an increased phosphorylation of troponin I and C-protein in isolated ventricular myocytes. Chelerythrine chloride attenuated the U50-dependent increases in troponin I and C-protein phosphorylation. These results indicate that k-opioid receptor dependent cardioprotection is mediated through a PKC-dependent modification of the myofilaments which slows the utilization of ATP by the actomyosin ATPase.
opioid, cardioprotection, preconditioning, heart, actin-myosin cycling, actomyosin MgATPase, protein kinase C, ATP, myofilaments, rats, Medical Physiology, Medical Sciences, Medicine and Health Sciences
University of Tennessee Health Science Center
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