Abstract: BACKGROUND: Exercise preconditioning produces early and late myocardial protective effects, in which protein kinase C and myocardial ATP-sensitive potassium channels (SarcKATP) are mediators and effectors, respectively. Protein kinase C regulates the expression of myocardial SarcKATP channels.
OBJECTIVE: To compare the effects of protein kinase C on the expression of myocardial SarcKATP channel subunits, inward recirculating potassium channel 6.2 (Kir6.2) and sulfonylurea receptor 2A (SUR2A), in exercise preconditioning.
METHODS: Forty-eight Sprague-Dawley rats were randomly divided into five groups: control group (no intervention), early exercise preconditioning group, protein kinase C inhibitor (pre-exercise intraperitoneal injection) + early exercise preconditioning group, late exercise preconditioning group, and protein kinase C inhibitor + late exercise preconditioning group. After preconditioning, the distribution and expression changes of Kir6.2 and SUR2A mRNAs in the rat myocardium were observed and detected using real-time fluorescent quantitative PCR. The distribution and expression changes of Kir6.2 and SUR2A proteins were observed and detected using western blot.
RESULTS AND CONCLUSION: (1) Compared with the control group, the mRNA expression of Kir6.2 and SUR2A showed no significant difference in the early and late exercise preconditioning groups. Compared with the early exercise preconditioning group, the protein kinase C inhibitor + early exercise preconditioning group showed a decrease in Kir6.2 mRNA expression and an increase in Kir6.2 protein expression, while both SUR2A mRNA and protein levels decreased. (2) Compared with the late exercise preconditioning group, the protein kinase C inhibitor + late exercise preconditioning group showed reduced Kir6.2 expression at mRNA and protein levels; meanwhile, SUR2A mRNA expression reduced and SUR2A expression increased. For the same subunit of myocardial Kir6.2 or SUR2A, protein kinase C exerts coordinated and complementary regulatory effects on its expression regulation in early and late exercise preconditioning, and as for different subunits of Kir6.2 and SUR2A, protein kinase C also has coordinated and complementary effects on their expression regulation in early and late exercise preconditioning.

Key words: protein kinase C, exercise preconditioning, myocardium, ATP-sensitive potassium channels, Kir6.2, SUR2A