[Electrophysiological analysis of the effects of 4-amino-pyridine in the isolated heart ventricle of the guniea pig].

The effects of 4-aminopyridine (4-AP) on guinea pig myocardial ventricular isolated strips were studied by means of intracellular microelectrodes. 4-AP increased the maximal depolarization velocity and decreased the effects of quinidine. In contrast to adrenaline, 4-AP antagonized the effects of MnCl1, but was ineffective against the alterations induced by a sodium poor solution. These findings support the suggestion that 4-AP modifies the electrophysiological membrane properties probably by increasing the Na+ inward current.