title: Phosphorylation of phosphatidylinositol by transverse tubule vesicles and its possible role in excitation-contraction coupling.
abstract: Phosphorylation of phosphatidylinositol to phosphatidylinositol 4-monophosphate and to phosphatidylinositol 4,5-bisphosphate was demonstrated in transverse-tubule membranes isolated from frog skeletal muscle using [gamma-32P]ATP as substrate. At millimolar concentrations of Mg2+ both phosphorylation reactions were completed within 15 s at 25 degrees C. Isolated sarcoplasmic reticulum vesicles phosphorylated phosphatidylinositol to phosphatidylinositol 4-phosphate with a lower specific activity than the transverse tubules, and lacked the ability to produce phosphatidylinositol 4,5-bisphosphate. These findings show, for the first time, that isolated transverse-tubule membranes carry out one of the steps required to sustain a role for inositol trisphosphate as the physiological messenger in excitation-contraction coupling in skeletal muscle. The finding that 0.5 mM tetracaine apparently inhibits the phosphorylation of phosphatidylinositol 4-phosphate to phosphatidylinositol 4,5-bisphosphate also supports a role for these intermediates in excitation-contraction coupling.
mesh_terms: D000818:Animals; D001001:Anura; D066298:In Vitro Techniques; D008274:Magnesium / Q000502:physiology; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism*; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013748:Tetracaine / Q000494:pharmacology
chemical_list: D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; C037178:phosphatidylinositol 4-phosphate; D013748:Tetracaine; D008274:Magnesium