The behavioral effects of the calcium agonist Bay K 8644 in the mouse: antagonism by the calcium antagonist nifedipine.

Mice injected with the calcium agonist BAY K 8644 (2-4 mg/kg, i.p.) displayed profound behavioral changes including ataxia, decreased motor activity, Straub tail, arched back, limb clonus and tonus, and an increased sensitivity to auditory stimulation. BAY K 8644 significantly impaired rotorod performance in mice with an ED50 of 0.8 mg/kg. The behavioral effects of BAY K 8644 were antagonized by nifedipine, but not by the non-dihydropyridine calcium channel antagonist verapamil or the alpha-adrenoceptor antagonist prazosin. Further, the actions of BAY K 8644 were not mimicked by the alpha-adrenoceptor agonist methoxamine at doses up to 4.5 mg/kg. These observations, coupled with the findings that BAY K 8644 is a potent, competitive inhibitor of [3H]nitrendipine binding to the dihydropyridine binding site in mouse brain (Ki = 7.0 X 10(-9) M), suggests that BAY K 8644 may produce its behavioral actions via an interaction with the DHP binding site, which has been linked to the control of calcium flux across membranes in peripheral tissues.