Distinct Occurrence of Phosphatidylinositol 4,5-Bisphosphate-Induced Ca2+ Release and Inositol 1,4,5-Triphosphate-Induced Release in ATP-Dependent Ca2+-Transporting Platelet Microsomes

• Published in: Journal of biochemistry (Tokyo) 1986-10, Vol.100 (4), p.911-921
• Main Authors: OHO, Chikara, TAKISAWA, Haruhiko
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Blood Platelets - drug effects; Blood Platelets - metabolism; Brain; Calcium - blood; Calcium-Transporting ATPases - blood; Cattle; Cell physiology; Fundamental and applied biological sciences. Psychology; Inositol 1,4,5-Trisphosphate; Inositol Phosphates - pharmacology; Kinetics; Membrane and intracellular transports; Microsomes - drug effects; Microsomes - metabolism; Molecular and cellular biology; Phosphatidylinositol 4,5-Diphosphate; Phosphatidylinositols - isolation & purification; Phosphatidylinositols - pharmacology; Sugar Phosphates - pharmacology
• ISSN: 0021-924X; 1756-2651
• DOI: 10.1093/oxfordjournals.jbchem.a121804

The effects of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) and inositol 1,4,5-triphosphate(InsP2) on the Ca2+ release from ATP-dependent Ca2+-transporting microsomes prepared from ox platelets were investigated. Under optimal conditions, both PtdInsP2 and InsP3 released Ca2+ from the microsomes in a similar dose-dependent manner. However, the maximal amount of Ca2+ released by InsP3 was almost one-fourth of that released by PtdInsP2. Neither PtdInsP, nor InsP3 appeared to act as a Ca2+ ionophore since they showed no effect on the Ca2+ content of liposomes prepared from platelet microsomal lipids. InsP3-induced but not PtdInsP2-induced Ca2+ release was decreased with increasing extravesicular Ca2+ from 0.1 μ to 10 μM and it was completely inhibited by 10 μM Ca2+. PtdInsP2-induced but not InsP3-induced Ca2+ release was markedly inhibited by Mg2+, ruthenium red and neomycin. In addition, InsP3 could induce no additional Ca2+ release after the accumulated Ca2+ had been maximally released by PtdInsP2. These results indicate that PtdInsP, releases Ca2+ from platelet microsomes more effectively than InsP3 by a mechanism distinct from that of InsP,-induced release, and further that InsP3-sensitive microsomes are included within the population of PtdlnsP3-sensitive microsomes.