Activation of alpha1B-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, Ca(2+) homeostasis via the epsilon isoform of protein kinase C (PKCepsilon) and mitoK(ATP) channels, may underlie the basis of alpha(1B)-AR-triggered cardioprotection.


METHODS
Indo-1 fluorescence in adult rat cardiomyocytes was used as an index of cytosolic ([Ca(2+)](c)) or mitochondrial free Ca(2+) concentration ([Ca(2+)](m)), and cell shortening was measured simultaneously. Cells were subjected to 20 min of simulated ischemia followed by 30 min of reperfusion (I/R).


RESULTS
Activation of a(1)-ARs by phenylephrine significantly decreased I/R-induced [Ca(2+)](c) and [Ca(2+)](m) overload, mitochondrial cytochrome c release and ATP reduction, and improved Ca(2+) transients and cell shortening. These protective effects were markedly inhibited by blockade of alpha(1B)-AR (chloroethylclonidine) but not alpha(1A)-AR (5'-methylurapidil) or alpha(1D)-AR (BMY 7378). Moreover, phenylephrine-afforded protection on the [Ca(2+)](m), [Ca(2+)](c), and cell shortening was lost when mitoK(ATP) channels were inhibited with 5-hydroxydecanoate and PKCepsilon with PKCepsilon V(1-2). However, PKCepsilon V(1-2) did not affect the mitoK(ATP) channel opener diazoxide-induced protection on these parameters.


CONCLUSIONS
These findings indicate that phenylephrine-induced protection on [Ca(2+)](m) homeostasis is mediated by selective activation of alpha(1B)-AR via mitoK(ATP) channel opening and PKCepsilon activation. Mitochondrial function appears to be a determinant of [Ca(2+)](c) and contractile function during I/R injury.
Gao
Hong
H
Laboratory of Molecular Cardiology, Institute of Health Sciences, Shanghai Institutes for Biological Sciences (SIBS), Chinese Academy of Sciences (CAS) and Shanghai Jiao Tong University School of Medicine (SJTUSM), Shanghai, 200025, China.
Chen
Le
L
Yang
Huang-Tian
HT
D000255:Adenosine Triphosphate / Q000378:metabolism; D058668:Adrenergic alpha-1 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D048429:Cell Size; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D006880:Hydroxy Acids / Q000494:pharmacology; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism*; D017202:Myocardial Ischemia / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000648:ultrastructure*; D010656:Phenylephrine / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism; D051744:Protein Kinase C-epsilon / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D015427:Reperfusion Injury / Q000378:metabolism / Q000517:prevention & control*; D014665:Vasodilator Agents / Q000494:pharmacology
C547718:Adra1b protein, rat; D058668:Adrenergic alpha-1 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D003652:Decanoic Acids; D006880:Hydroxy Acids; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D018340:Receptors, Adrenergic, alpha-1; D014665:Vasodilator Agents; D010656:Phenylephrine; C051731:chlorethylclonidine; C052853:5-hydroxydecanoic acid; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D051744:Protein Kinase C-epsilon; D003000:Clonidine; D003981:Diazoxide; D002118:Calcium