Cellular mechanism of action of cognitive enhancers: Effects of nefiracetam on neuronal Ca2+ channels

Cellular mechanisms underlying the cognition-enhancing actions of piracetam -like nootropics were studied by recording Ca2+ channel currents from neuro blastoma x glioma hybrid (NG108-15) cells and Xenopus oocytes expressing Ca 2+ channels. In NG108-15 cells, nefiracetam (1 mu M) produced a twofold inc rease in L-type Ca2+ channel currents. A similar. but slightly less potent effect was observed with aniracetam. whereas piracetam and oxiracetam exert ed no such effects. Cyclic AMP analogs mimicked the nefiracetam action. N-t ype Ca2+ channel currents inhibited by leucine (Leu)-enkephalin by means of inhibitory G proteins (Go/Gi) were recovered promptly by nefiracetam, wher eas those inhibited by prostaglandin E1 via stimulatory G proteins were not affected by nefiracetam. Cells treated with pertussis toxin (500 ng/mL, > 20 hours) were insensitive to nefiracetam. In Xenopus oocytes functionally expressing N-type (alpha(1B)) Ca2+ channels and delta-opioid receptors, nef iracetam was also effective in facilitating the recovery from Leu-enkephali n-induced inhibition. These results suggest that nefiracetam, and possibly aniracetam, may activate N- and L-type Ca2+ channels in a differential way depending on how they recover from Go/Gi-mediated inhibition.