Title

k-Opioid Receptor Dependent Cardioprotection in the Rat

Date of Award

12-1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Program

Physiology

Research Advisor

Polly A. Hofmann, Ph.D.

Committee

Aviv I. Hassid, Ph.D. K. U. Malik, Ph.D. Gabor Tigyi, M.D., Ph.D. Donald B. Thomason, Ph.D.

Abstract

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.

DOI

10.21007/etd.cghs.1999.0255

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