Influence of Ca2+ channel modulators on [3H]purine release from rat cultured glial cells.

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