3,4-DIAMINOPYRIDINE INDUCED HYDROLYSIS OF PHOSPHOINOSITIDE IN CULTURED NEURONS FROM EMBRYO CHICK FOREBRAIN

The effect of 3,4-diaminopyridine (DAP) on phosphoinostide hydrolysis in cultured neurons from embryo chick forebrain has been studied. DAP produced a dose- and time-dependent accumulation of inositol phosphate s. At 1mM DAP a maximal effect was obtained. In Ca2+ free medium, DAP- activated turnover of phosphoinositide was reduced, but was still sign ificant. Blocking Ca2+ entry with 200 mu M Cd2+ also did not abolish t he DAP-induced accumulation of inositol phosphates. As a comparison th e effect of high K+ exposure was investigated. High K+ enhanced phosph oinositide hydrolysis, and this effect was also reduced by excluding C a2+ influx. Moreover, DAP had no additional effect on the high K+-indu ced hydrolysis of phosphoinositide. Using oxonol-V, a depolarization o f the membrane potential was seen in the neurons bathed in DAP contain ing medium. It is suggested that the depolarization may play a role in DAP-activated phosphoinositide turnover in cultured neurons of the em bryo chick forebrain, but that Ca2+ entry is not necessary for this ef fect.