title: Stimulatory effect of hormonal signaling factors on (Ca(2+)-Mg2+)-ATPase activity in rat liver plasma membranes: cross talk with regucalcin.
abstract: The effect of hormonal signaling factors on (Ca(2+)-Mg2+)-ATPase activity in rat liver plasma membranes was investigated. The presence of inositol-glycan (10(-7)-10(-5) M), dibutyryl cAMP (10(-4) and 10(-3) M) or inositol 1,4,5-trisphosphate (IP3; 10(-6) and 10(-5) M) in the enzyme reaction mixture produced a significant increase in (Ca(2+)-Mg2+)-ATPase activity. These effects were completely inhibited by the presence of vanadate (10(-4) M), an inhibitor of the enzyme phosphorylation, and N-ethylmaleimide (5 x 10(-3) M), a SH group modifying reagent. Meanwhile, regucalcin, a Ca(2+)-binding protein isolated from rat liver cytosol, increased the enzyme activity by binding to the SH groups of (Ca(2+)-Mg2+)-ATPase in liver plasma membranes. The presence of regucalcin (0.25 microM) with an effective concentration completely inhibited the effect of inositol-glycan (10(-5) M) to increase (Ca(2+)-Mg2+)-ATPase activity, while the effect of dibutyryl cAMP (10(-3) M) or IP3 (10(-5) M) was not altered. The inositol-glycan effect was not modulated by the presence of dibutyryl cAMP or IP3. Now, the preincubation of the plasma membranes with regucalcin did not modify the effect of inositol-glycan on the enzyme activity, suggesting that regucalcin competes with inositol-glycan for the binding to the plasma membranes. The present results suggest that there may be a cross talk with regucalcin and hormonal signaling factors in the regulation of (Ca(2+)-Mg2+)-ATPase activity in liver plasma membranes.
authors.affiliation: Laboratory of Metabolism and Endocrinology, Graduate School of Nutritional Sciences, University of Shizuoka, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Takahashi
authors.forename: S
authors.initials: S
authors.lastname: Suzuki
authors.forename: M
authors.initials: M
authors.lastname: Yamaguchi
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D017301:Ca(2+) Mg(2+)-ATPase / Q000187:drug effects*; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D002265:Carboxylic Ester Hydrolases; D002462:Cell Membrane / Q000187:drug effects; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007294:Inositol / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D008099:Liver / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D011134:Polysaccharides / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D015238:Sulfotransferases
chemical_list: D002135:Calcium-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D011134:Polysaccharides; C068698:inositol-glycan; D007294:Inositol; D003994:Bucladesine; D015544:Inositol 1,4,5-Trisphosphate; D006160:Guanosine Triphosphate; D015238:Sulfotransferases; C028152:alcohol sulfotransferase; D002265:Carboxylic Ester Hydrolases; C513325:Rgn protein, rat; D017301:Ca(2+) Mg(2+)-ATPase