3,4-Diaminopyridine induced hydrolysis of phosphoinositide in cultured neurons from embryo chick forebrain.

The effect of 3,4-diaminopyridine (DAP) on phosphoinositide hydrolysis in cultured neurons from embryo chick forebrain has been studied. DAP produced a dose- and time-dependent accumulation of inositol phosphates. At 1 mM DAP a maximal effect was obtained. In Ca2+ free medium, DAP-activated turnover of phosphoinositide was reduced, but was still significant. Blocking Ca2+ entry with 200 microM Cd2+ also did not abolish the DAP-induced accumulation of inositol phosphates. As a comparison the effect of high K+ exposure was investigated. High K+ enhanced phosphoinositide hydrolysis, and this effect was also reduced by excluding Ca2+ influx. Moreover, DAP had no additional effect on the high K(+)-induced hydrolysis of phosphoinositide. Using oxonol-V, a depolarization of the membrane potential was seen in the neurons bathed in DAP containing medium. It is suggested that the depolarization may play a role in DAP-activated phosphoinositide turnover in cultured neurons of the embryo chick forebrain, but that Ca2+ entry is not necessary for this effect.