Effect of Stimulation of α-Adrenergic Receptors on Action Potential of Working Cardiomyocytes in Rat Atrium.

The study examined the effect of clonidine hydrochloride (10-10 М) on electrical activity of working cardiomyocytes in rat right atrium. Stimulation of α-adrenergic receptor with clonidine changed electrical activity of the heart. All tested concentrations of the agonist lengthened the action potential and decreased the firing rate of cardiomyocytes in a dose-dependent manner.

Effect of If Current Blockade on Newborn Rat Heart Isolated According to Langendorff.

The study examined the effects of hyperpolarization-activated funny current (If) on HR and coronary flow in Langendorff-isolated hearts from newborn rats. Blockade of If current with ZD7288 changed the examined cardiac parameters. The blocker in a concentration of 10 M decreased HR by 26.

Effect of α-Adrenoceptor Stimulation on Functional Parameters of Langendorff-Isolated Rat Heart.

We studied the effect of α-adrenoreceptor agonist clonidine hydrochloride in concentrations of 10-10 M on inotropy, chronotropy, and coronary flow in Langendorff-isolated heart of adult rats. It was found that α-adrenoreceptor agonist changed all studied parameters. Left ventricular myocardium contraction force decreased after application of all tested concentrations, the maximum effect was observed at a concentration of 10 M.

Changes in electrical activity of working myocardium under condition of if current inhibition.

The study examined the effect of ZD7288, a blocker of hyperpolarization-activated "funny" current If, on electrical activity in working atrial and ventricular myocardium in rats. In concentrations range from 3×10(-6) to 3×10(-5) M, the agent significantly increased the duration of action potentials at 50 and 90% repolarization levels in both atrial and ventricular myocardium at the fixed stimulation rate of 5 Hz. The blocker affected neither resting potential nor the upstroke velocity of action potential.