INFLUENCE OF CA2+ CHANNEL MODULATORS ON [H-3] PURINE RELEASE FROM RAT CULTURED GLIAL-CELLS

[H-3]Purine release from rat striatum astrocyte cultures was studied at 14 days in vitro (DIV). Superfusion of cultures with a Ca2+-free medium + 0.5 mM ethylene glycol-bis(beta-aminoethyl-ether)N,N,N',N'-tetracetic acid (EGTA) reduced the electrically evoked [H-3]purine release. Nimodipine only at the concentration of 10 mu M modified [H-3]purine outflow whereas 0.1 mu M omega-conotoxin and 0.03-0.1 mu M nitrendipine reduced the evoked one. Superfusion of cultures with 0.1 mu M omega-conotoxin + 0.1 mu M nitrendipine antagonized the evoked [H-3]purine release similarly to each drug given alone. Neither nitrendipine nor omega-conotoxin influenced the uptake of Ca-45(2+) by the cultures. The treatment of cells with the Ca2+ agonist Bay K 8644 did not affect [H-3]purine release or the Ca-45(2+) uptake. The drug did not either alter [Ca2+](i), evaluated by loading the cells with 3 mu M Fura-2/AM. 10-30 mu M 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8), a blocker of intracellular Ca2+ discharge, significantly reduced the evoked [H-3]purine release. On the other hand, 2 mu M thapsigargin, an inhibitor of the ion store Ca2+ ATPase, was able to increase either the culture [H-3]purine release or the [Ca2+](i). Together, the findings indicate that voltage-sensitive calcium channels (VSCCs) of the neuronal N and L-types are not involved in the modulation of [H-3]purine release from rat cultured astrocytes whereas Ca2+ coming from intracytoplasmic stores seems to play a prevailing role. Moreover, agents which block VSCCs seem to be able to affect [H-3]purine outflow with mechanisms other than VSCC gating.