INOSITOL TRISPHOSPHATE, POLYPHOSPHOINOSITIDE TURNOVER, AND HIGH-ENERGY METABOLITES IN FOCAL CEREBRAL-ISCHEMIA AND REPERFUSION

Background and Purpose Although the signaling pathway involving polyph osphoinositide (poly-PI) hydrolysis and release of inositol 1,4,5-tris phosphate [Ins(1,4,5)P-3] is an important mechanism for regulation of neuronal calcium homeostasis, the effect of cerebral ischemia-reperfus ion on this calcium signaling pathway is not well understood. Because activity of this pathway is dependent on availability of ATP, this stu dy is aimed at examining the poly-PI signaling pathway and high energy metabolites in a rat stroke model. Methods Focal cerebral ischemia in rats was induced by temporary occlusion of the right middle cerebral artery and both common carotid arteries. Levels of Ins(1,4,5)P-3 were determined by use of the radioreceptor binding assay. Poly-PI turnover in rat cortex was assessed with an in vivo protocol involving intrace rebral injection of [H-3]inositol and systemic administration of lithi um. High-energy metabolites (ATP, ADP, and AMP) were analyzed by high- performance liquid chromatography. Results Ischemia induced an increas e in poly-PI turnover in the right middle cerebral artery cortex, but reperfusion led to a decline in this signaling activity. However, Ins( 1,4,5)P-3 levels decreased during ischemia, and these levels were not restored if ischemic insults were longer than 30 minutes. ATP levels d ecreased to 26% of control during ischemia and recovered to 80% of con trol during the initial 3 hours of reperfusion; these changes were fol lowed by a second phase of decline. Conclusions Results show an import ant relationship between een ischemia-induced depletion of high-energy metabolites and poly-PI signaling activity. However, the uncoupling b etween Ins(1,4,5)P-3 and ATP during reperfusion after severe ischemia suggests that metabolism of Ins(1,4,5)P-3 is more stringently regulate d than ATP.