The Cardioprotective Effect Persisting During Recovery From Cold Acclimation Is Mediated By The Beta(2)-Adrenoceptor Pathway And Akt Activation

The infarct size-limiting effect elicited by cold acclimation (CA) is accompanied by increased mitochondrial resistance and unaltered beta(1)-adrenergic receptor (AR) signaling persisting for 2 wk at room temperature. As the mechanism of CA-elicited cardioprotection is not fully understood, we examined the role of the salvage beta(2)-AR/G(i)/Akt pathway. Male Wistar rats were exposed to CA (8 degrees C, 5 wk), whereas the recovery group (CAR) was kept at 24 degrees C for additional 2 wk. We show that the total number of myocardial beta-ARs in the left ventricular myocardium did not change after CA but decreased after CAR. We confirmed the infarct size-limiting effect in both CA and CAR groups. Acute administration of beta(2)-AR inhibitor ICI-118551 abolished the protective effect in the CAR group but had no effect in the control and CA groups. The inhibitory G(i)alpha(1/2) and G(i)alpha(3) proteins increased in the membrane fraction of the CAR group, and the phospho-Akt (Ser(473))-to-Akt ratio also increased. Expression, phosphorylation, and mitochondrial location of the Akt target glycogen synthase kinase (GSK-3 beta) were affected neither by CA nor by CAR. However, GSK-3 beta translocated from the Z-disk to the H-zone after CA, and acquired its original location after CAR. Our data indicate that the cardioprotection observed after CAR is mediated by the beta 2-AR/G(i) pathway and Akt activation. Further studies are needed to unravel downstream targets of the central regulators of the CA process and the downstream targets of the Akt protein after CAR.NEW & NOTEWORTHY Cardioprotective effect of cold acclimation and that persisting for 2 wk after recovery engage in different mechanisms. The beta(2)-adrenoceptor/G(i) pathway and Akt are involved only in the mechanism of infarct size-limiting effect occurring during the recovery phase. GSK-3 beta translocated from the Z-line to the H-zone of sarcomeres by cold acclimation returns back to the original position after the recovery phase. The results provide new insights potentially useful for the development of cardiac therapies.