P2X7 receptors exert a permissive effect on the activation of presynaptic AMPA receptors in rat trigeminal caudal nucleus glutamatergic nerve terminals

摘要

Effects of purinergic receptor agonists on basal and 12 mM [K+]e-evoked [3H]D-ASP release from rat TCN synaptosomes. a Effects of ATP on basal and [K+]e-evoked release of [3H]D-ASP. Synaptosomes prelabeled with [3H]D-ASP were superfused with standard medium at a flow rate of 0.6 ml/min. At the beginning of min 38 (arrow), the medium was replaced with standard medium containing ATP (1 mM) or depolarizing medium (12 mM [K+]e) plus ATP (1 mM) (arrow) and perfusion continued for 4 min (i.e., minute 38 through min 41). Radioactivity in each fraction has been expressed as a percentage of the total radioactivity content present in the tissue at the onset of the fraction collected. Each point represents the mean ± S.E.M. of 3–4 different experiments, each run in triplicate (3 superfusion chambers for each condition). Error bars are absent when the S.E.M. was smaller than the symbol used in the graph. b Log concentration-response curves for BzATP in evoking [3H]D-ASP efflux and its Mg2+ sensitivity. BzATP (0.01–3 mM) was present in the standard perfusion medium for 4 min (min 38 through min 41). To assess the Mg2+–sensitivity of the effects of BzATP, synaptosomes were perfused for 18 min (min 20 through min 37) with standard medium in which the Mg2+ concentration had been reduced from 1.2 mmol/L to 0.01 mmol/L and then with the same medium containing BzATP (min 38 through min 41). The effects of the BzATP were expressed as percentage increases (ratio of the AUC observed in the presence of BzATP to the AUC for the release observed in the absence of the agonist). Data are means ± S.E.M. of at least 3 experiments, each run in triplicate. *P < 0.05 vs basal release. c Effects of ATP and BzATP on basal [3H]D-ASP release and their antagonism by A438079. A438079 (5 μM) was added to the perfusion medium 8 min before the agonists. ATP (1 mM) or BzATP (100 μM) was present in the standard perfusion medium (with or without A438079) for 4 min (minutes 38 through 41). Results are expressed as areas under the release/time-curves (AUCs). Each bar represents the mean ± SEM of 3 different experiments, each run in triplicate. *P < 0.05 vs basal release