Organic calcium channel blockers enhance [3H]purine release from rat brain cortical synaptosomes

The release of ³H]purines was investigated in a crude mitochondrial fraction (P₂ fraction) from rat brain cortex pre-loaded with ³H]adenosine for 30 sec at 37°C in vitro. Potassium, veratridine and glutamate were used as depolarizing agents to evoke the release of ³H]purines. Ca²⁺ removal, the addition of EGTA, and treatment with organic or inorganic Ca²⁺ antagonists did not inhibit ³H]purine release in this preparation. On the other hand, Ca²⁺ removal and the addition of EGTA greatly enhanced³H-purine release induced by glutamate. D-600 and diltiazem enhanced K⁺-evoked ³H]purine release, and nifedipine increased veratridine evoked ³H]purine release indicating that either these Ca²⁺ antagonists have different sites of action, or that K⁺ and veratridine may release ³H]purine from different metabolic pools. Organic Ca²⁺ antagonists failed to enhance the ³H]purine release evoked by glutamate, further supporting the notion that various depolarizing agents may release ³H]purines from different cellular compartments.