The neurotoxins, batrachotoxin and veratridine, are specific activators of sodium channels and cause an increase in the rate of 22Na uptake in neuroblastoma cells. Yohimbine, an indolakylamine alkaloid, inhibits this batrachotoxin-induced 22Na uptake. The dose-response curve of yohimbine suggest that the inhibitor acts reversibly on a single class of binding sites with dissociation constant of 3--4 x 10(-5) M. The dissociation constant is not affected by depolarization from--41 to 0 mV. Kinetic and equilibrium experiments indicate that yohimbine is a competitive inhibitor of the action of batrachotoxin. These results support the conclusion that yohimbine inhibitis the sodium flux by acting on the channel gating mechanism rather than by occluding the channels.
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