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

Compared with N-methyl-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.