GLUTAMATE SELECTIVELY INCREASES THE HIGH-THRESHOLD CA2+ CHANNEL CURRENT IN SENSORY AND HIPPOCAMPAL-NEURONS

Previous studies resulted in conflicting conclusions that glutamate application either decreases or increases the activity of Ca2+ channels in hippocampal neurons. We studied whole-cell Ca2+ currents (I(Ca)) in chick dorsal root ganglion neurons and rat hippocampal cells. For both cell types glutamate (1-30-mu-M) increased high-threshold Ca2+ current. It was independent of the charge carriers, Ca2+ or Ba2+. Low-threshold Ca2+ channel current and the fast sodium current were not changed with glutamate application. The effect developed within 1-2 min and then further facilitated after washout of the agonist. A second application of glutamate produced no additional increase in I(Ca). No changes in the time-course of whole-cell currents were observed, suggesting that glutamate recruits 'sleepy' Ca2+ channels. Whatever its mechanism, overlasting increase of I(Ca) by glutamate may be important in neuronal plasticity.