Adenophostin-medicated quantal Ca 2+ release in the purified and reconstituted inositol 1,4,5-trisphosphate receptor type 1

Abstract

Kinetics of Ca 2+ release by adenophostin, a novel agonist of inositol 1,4,5-trisphosphate (IP 3) receptor, in the purified and reconstituted IP 3 receptor type 1 (IP 3R1) was investigated using the fluorescent Ca 2+ indicator fluo-3. Submaximal concentrations of adenophostin caused quantal Ca 2+ release from the purified IP 3R1 as IP 3 did. Adenophostin-induced Ca 2+ release by the purified IP 3R1 exhibited a high positive cooperativity (nH = 3.9 ± 0.2, EC 50 = 11 nM), whereas the IP 3-induced Ca 2+ release exhibited a moderate one ( nH = 1.8 ± 0.1, EC 50 = 100 nM). Inhibition of [ 3H]IP 3 binding to the purified IP 3R1 by adenophostin exhibited a positive cooperativity ( nH = 1.9, K i = 10 nM), whereas IP 3 did not ( nH = 1.1, K i = 41 nM).