Activation of α1B-adrenoceptors alleviates ischemia/reperfusion injury by limitation of mitochondrial Ca2+ overload in cardiomyocytes

Objective: Activation of (alpha(1)-adrenergic receptors (alpha(1)-ARs) mimics ischemic preconditioning (IP). However, the subtypes of alpha(1)-ARs involved and the protective mechanisms are not entirely clear. Here we tested the hypothesis that preservation of mitochondrial integrity, in particular, Ca2+ homeostasis via the epsilon isoform of protein kinase C (PKC epsilon) and mitoK(ATP) channels, may underlie the basis of a alpha(1)-AR-triggered cardioprotection. Methods: Indo-1 fluorescence in adult rat cardiomyocytes was used as an index of cytosolic ([Ca2+](c)) or mitochondrial free Ca2+ concentration ([Ca2+].), and cell shortening was measured simultaneously. Cells were subjected to 20 min of simulated ischemia followed by 30 min of reperfusion (LR). Results: Activation of alpha(1)-ARs by phenylephrine significantly decreased I/R-induced [Ca2+](c) and [Ca2+] overload, mitochondrial cytochrome c release and ATP reduction, and improved Ca2+ transients and cell shortening. These protective effects were markedly inhibited by blockade of (alpha(1B)-AR (chloroethylclonidine) but not (alpha(IA)-AR (5'-methylurapidil) or alpha(ID)-AR (BMY 7378). Moreover, phenylephrine-afforded protection on the [Ca2+](m), [Ca2+](c), and cell shortening was lost when mitoKATp channels were inhibited with 5-hydroxydecanoate and PKC epsilon with PKC epsilon V1-2. However, PKC epsilon V1-2 did not affect the mitoKATp channel opener diazoxide-induced protection on these parameters. Conclusions: These findings indicate that phenylephrine-induced protection on [Ca2+](m) bomeostasis is mediated by selective activation of alpha(1B)-AR via mitoKATp channel opening and PKC epsilon; activation. Mitochondrial function appears to be a determinant of [Ca2+](c) and contractile function during I/R injury. (c) 2007 European Society of Cardiology. Published by Elsevier B.V All rights reserved.