BACLOFEN INHIBITS HIGH-THRESHOLD CALCIUM CURRENTS WITH 2 DISTINCT MODES IN RAT HIPPOCAMPAL-NEURONS

In primary cultures of hippocampal neurons, activation of GABA, recept ors reversibly inhibits high-voltage activated (HVA) Ca currents. In s ome neurons the GABA(B) agonist baclofen produces slow down of Ca curr ent activation. In these cells the inhibitory action of the agonist ca n be relieved by strong pre-conditioning depolarizations. In other cel ls, where no significant changes in activation kinetics could be obser ved during agonist application, conditioning prepulses are nearly inef fective to recover the current from inhibition. Thus, in hippocampal n eurons, activation of GABAergic receptors can modulate Ca currents wit h two different modes: one is voltage-dependent and the other is volta ge-independent. In the presence of omega-conotoxin (omega-CgTx), only the second mode is prevented, suggesting that the two modulatory mecha nisms (voltage-dependent and voltage-independent) operate in different cells on separate classes of HVA Ca channels.