Myocardial infarction is coupled with activation of cyclins and cyclin-dependent kinases in myocytes.

To determine whether the molecular components implicated in the regulation of the cell cycle are activated in myocytes after infarction, the expression of cyclins E, A, and B and the levels of their associated kinase activity were measured at 1 and 7 days following surgery. The quantity of cdk2 and cdc2 and the level of their kinase activity were also determined. Myocardial infarction was characterized by an increase in cyclins E, A, and B and cdc2 proteins in the surviving myocytes at 1 and 7 days. Cyclin E, A, and B and cdk2 and cdc2 kinase activity also increased. The quantity of cyclins E and A and the level of cyclin E-associated kinase activity in myocytes after infarction were comparable with those measured in neonatal myocytes. Moreover, cdc2 protein and cdc2 kinase activity in myocytes reached levels after infarction which were similar to those in neonatal myocytes. Thus, myocytes react to myocardial infarction by activating cyclins and cyclin-dependent kinases which may be coupled with the regeneration of muscle mass and recovery of ventricular function.