2 COMPONENTS OF GLUTAMATE EXOCYTOSIS DIFFERENTIALLY AFFECTED BY PRESYNAPTIC MODULATION

The total Ca2+-dependent release of glutamate induced by depolarizatio n of cerebrocortical nerve terminals with KCI was analyzed into a fast and a slow component. The fast component exhibited a decay time of <1 s and accounted for 0.95 +/- 0.10 nmol of glutamate, whereas the slow component, which exhibited a decay time of 52 +/- 7 s, accounted for the release of 2.48 +/- 0.19 nmol of glutamate. These two components w ere differentially affected by the Ca2+ chelator BAPTA, the divalent c ation Sr2+,, the botulinum neurotoxin A. The adenosine A, receptor ago nist NG-cyclohexyladenosine strongly reduced the fast component withou t altering the slow component, In contrast, the inhibitory effect of a rachidonic acid and the facilitatory action of the metabotropic glutam ate receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid were observed as a decrease and an increase, respectively, in the two components. It is concluded, first, that the fast and slow components correspond to the release of docked and mobilized vesicles, respectiv ely, and second, that presynaptic modulation more significantly alters the fast component of release.