Calcium pools mobilized by calcium or inositol 1,4,5-trisphosphate are differentially localized in rat heart and brain.

Calcium-induced calcium release (CICR) pools have been demonstrated in brain and heart microsomes biochemically and autoradiographically by the sensitivity of 45Ca2+ accumulation to Mg2+, ATP, ruthenium red, caffeine, and tetracaine. The CICR pool colocalizes with [3H]ryanodine binding sites, supporting the notion that [3H]ryanodine labels CICR pools. Sites of CICR pools in the brain contrast with those of inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ pools with reciprocal localizations between the two Ca2+ pools in several structures. Thus, in the hippocampus CA-1 is enriched in IP3-sensitive Ca2+ pools, whereas CICR pools are highest in CA-3 and the dentate gyrus. The corpus striatum and cerebellum are enriched in IP3 pools, whereas the medial septum and olfactory bulb have high CICR densities. In cardiac tissue, CICR is localized to atrial and ventricular muscle, whereas IP3 pools are concentrated in coronary vessels and cardiac conduction fibers. The reciprocal enrichment of IP3 and CICR Ca2+ pools implies differential regulation of Ca2+ hemostasis in these tissues.