Potentiation of vasoconstrictor responses by 3- and 4-aminopyridine.

1. In concentrations that are known to reduce potassium conductance in many excitable membranes, 3 and 4-aminopyridine (3-AP, 4-AP) potentiate vasoconstrictor responses of the isolated ear artery of the rabbit to noradrenaline and histamine. 2. 3- and 4-AP have no effect on the responses of potassium-depolarized arteries to noradrenaline, histamine or calcium. 3. The results suggest that the aminopyridines have no direct effect on the contractile machinery or on pharmacomechanical coupling, but cause potentiation by influencing electrical events at the cell membrane. 4. 4-AP causes a greater potentiation of the response te electrical stimulation than of the response to noradrenaline. This suggests that the aminopyridines may also cause an increase in the amount of noradrenaline released in response to sympathetic nerve stimulation.