[4-Aminopyridine induced histamine release and its antagonism by certain drugs]

4-Aminopyridine (4-AP), a known potassium channel blocker, was shown to induce histamine release from mast cells in mice. After ip 4-AP 5 mg.kg-1 the histamine content increased in blood, but decreased in the lung tissue. Calcium antagonists nifedipine (NIF) 500 mg.kg-1 ig, TMB-8 300 mumol.L-1 in vitro and potassium channel opener minoxidil (MIN) 100 mg.kg-1 inhibited the histamine release induced by 4-AP from mouse peritoneal mast cells (PMC). These results provide evidence that potassium channels are present in mouse mast cell membranes and indicate that the mechanism of histamine release by 4-AP may be related to the potassium channel blocking effect. As the result of this effect, the calcium channels open and the Ca2+ influx to the mast cells increases, thus eliciting histamine release.