α1A- but not α1B-adrenergic receptors precondition the ischemic heart by a staurosporine-sensitive, chelerythrine-insensitive mechanism

Objective : Brief periods of ischemia stimulate an endogenous mechanism in the heart that protects the myocardium from subsequent ischemic injury. α1-Adrenergic receptors (ARs) have been implicated in this process. However, the lack of sufficiently selective antagonists has made it difficult to determine which α1-AR subtype protects the heart from ischemic injury. The goal of this study was to identify the α1-AR subtype that is involved in ischemic preconditioning. Methods : We developed transgenic mice that express constitutively active mutant (CAM) forms of the α1A-AR or the α1B-AR regulated by their endogenous promoters. Hearts isolated from transgenic and non-transgenic mice were perfused by the Langendorff method using an ischemic preconditioning perfusion protocol or a non-preconditioning perfusion protocol prior to 30-min ischemia and 40-min reperfusion. Contractile function was continuously monitored through an intraventricular balloon. Results : The contractile function of non-transgenic hearts perfused according to the ischemic preconditioning protocol completely recovered from 30-min ischemia. However, non-transgenic hearts perfused according to the non-preconditioning protocol recovered only 60% of their contractile function. The contractile function of CAM α1A-AR hearts, but not CAM α1B-AR hearts, completely recovered from 30-min ischemia even though they were perfused according to the non-preconditioning protocol. Thus, CAM α1A-AR hearts, but not CAM α1B-AR hearts, were inherently preconditioned against ischemic injury. Staurosporine, but not chelerythrine, completely reversed the preconditioning effect of CAM α1A-ARs. Conclusions : These data demonstrate that α1A-ARs protect the heart from ischemic injury through a staurosporine-sensitive signaling pathway that is independent of protein kinase C.