In Vitro Binding of [ 3H]Nimodipine and [ 3H]CGS-19755 to Rat Brain in Focal Cerebral Ischemia

Abstract

Focal cerebral ischemia results in increased in vivo binding of calcium channel antagonists to both the L-type voltage sensitive calcium channel (VSCC) and the N-methyl- d-aspartate (NMDA) receptor-linked calcium channel. It was the aim of this study to investigate the effect of focal cerebral ischemia on the in vitro binding of calcium channel antagonists to rat brain. Quantitative autoradiography was used to measure regional in vitro binding of the L-type VSCC antagonist [ 3H]nimodipine and the competitive NMDA receptor antagonist [ 3H]CGS-19755 to rat brain following 4 h of irreversible focal cerebral ischemia. [ 3H]Nimodipine binding to the nonischemic hemisphere was characterized by one binding site with regional binding affinity ( K D ) estimates ranging from 221 to 482 p M and maximal binding site densities ( B max ) ranging from 13.2 (9.6-17.5) pmol/g tissue (estimate and 95% confidence interval) in CA1 to 32.5 (26.5-39.9) pmol/g tissue in dentate. [ 3H]CGS-19755 binding to the nonischemic hemisphere was characterized by K D estimates ranging from 59 to 97 n M and B max values ranging from 143 (108-192) pmol/g tissue in cortex to 569 (515-641) pmol/g tissue in CA1. For [ 3H]CGS-19755 a model of two binding sites was applicable in several brain regions. No difference in binding site densities or binding affinities between ischemic and paired nonischemic structures (cortex and striatum) was observed with either ligand. In vitro binding of [ 3H]nimodipine and [ 3H]CGS-19755 to ischemic brain failed to identify ischemic-induced changes in calcium channel function previously reported by in vivo binding methods.