Mitochondrial ATP-sensitive K
+ (mitoK
ATP) and Ca
2+-activated K
+ (mitoK
Ca) channels exist in cardiac myocytes, and they play key roles in cardioprotection. We have recently reported that K
+ influx through mitoK
ATP or mitoK
Ca channels occurs independently of each other and confers cardioprotection in a similar manner. Activation of mitoK
ATP channel is augmented by protein kinase C (PKC), whereas mitoK
Ca channel is activated by protein kinase A (PKA). However, phosphatidylinositol 3-kinase (PI3-K) is linked to neither mitoK
ATP nor mitoK
Ca channels. We have demonstrated that bioactive substances modulate the opening of mitoK
ATP channels via a PKC-dependent pathway or opening of mitoK
Ca channels via a PKA-dependent pathway and thereby protecting the heart from ischemia/reperfusion injury. Several endogenous substances such as adenosine and bradykinin can reduce infarct size by activation of mitoK
ATP channels in a PKC-dependent manner. Adrenomedullin, a potent vasodilator peptide, potentiates the opening of mitoK
Ca channels by PKA activation. Treatment with adrenomedullin prior to ischemia results in the reduction of infarct size via a PKA-mediated activation of mitoK
Ca channels. Thus, some endogenous substances confer cardioprotection via PKA- or PKC-mediated activation of mitoK
ATP or mitoK
Ca channels.
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