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 I f , 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. In patch-clamp experiments, ZD7288 selectively inhibited I f current, but produced no effect on delayed rectifier potassium currents that determine the rate of repolarization. The described effects of ZD7288 are not related to its non-specific effects on the ionic currents except I f .