Electrical Activity of Right Atrial Cardiomyocytes in Rats with Experimental Myocardial Infarction After α-Adrenoceptors Stimulation

This study investigates the effects of the α₁-adrenergic receptor agonist methoxamine at a concentration of 10⁻⁸ M on the frequency and characteristics of spontaneous action potentials in right atrial preparations of healthy rats and those with experimental MI (acute phase: 1 day; chronic phase: 54 days). Methoxamine significantly increased the spontaneous activity frequency across all groups. Crucially, the ability of methoxamine to shorten the AP duration (APD) was significantly attenuated in the infarcted myocardium. The APD shortening effect was most pronounced in healthy controls and markedly weaker in both the acute and chronic MI groups. These findings highlight the significant functional remodeling of the cardiac α₁- adrenergic system post-MI. The attenuated repolarization response suggests that regulatory mechanisms are compromised, potentially contributing to the electrophysiological instability and heightened arrhythmia risk observed after myocardial infarction.