Block of kainate receptor channels by Ca2+ in isolated spinal trigeminal neurons of rat.

Compared with N-methyl-D-aspartate-activated channels, the interaction of Ca2+ with kainate-activated or with quisqualate-activated channels is not well understood. We have studied the effect of Ca2+ on kainate-activated currents in isolated trigeminal neurons and found that Ca2+ inhibits kainate responses. This inhibition occurs not because Ca2+ changes the affinity of kainate to its receptor, but because Ca2+ blocks monovalent cation permeation through kainate-activated channels. This Ca2+ block gives rise to the outward rectification of the kainate responses.