Ca2+-stimulated phospholipid phosphoesterase activities in rabbit erythrocyte membranes.
The properties of the enzymes involved in Ca2+-stimulated breakdown of phosphatidylinositol 4'-phosphate (PIP), phosphatidylinositol 4',5'-bisphosphate (PIP2), and phosphatidic acid (PA) in rabbit erythrocyte ghosts were studied. At 25 degrees C, 1 to 180 microM Ca2+ rapidly stimulated the breakdown of PIP and PIP2, and maximal breakdown occurred within 10 minutes at all Ca2+ concentrations. The rate and the total amount of breakdown of PA, PIP, and PIP2 increased with Ca2+ concentration. MgCl2 inhibited the rate of Ca2+-stimulated breakdown of PIP and PIP2 at Ca2+ concentrations less than 10 microM, but did not have any appreciable effects at higher Ca2+ concentrations. MgCl2 also protected against Ca2+-stimulated breakdown of PA. In the presence and absence of 5 mM MgCl2, Ca2+ stimulated half-maximal breakdown of PIP and PIP2 at 2-3 microM under hypotonic and isotonic conditions. In the presence of 5 mM MgCl2, Ca2+-stimulated breakdown of PIP and PIP2 was associated with the release of Pi and inositol bisphosphate. In the absence of MgCl2, Ca2+ stimulated the release of 32P-labeled Pi, inositol bisphosphate, and inositol trisphosphate from labeled PIP, PIP2, and PA. Ca2+ increased phosphatidylinositol content and decreased PIP and PIP2 content in these membranes. The results of this investigation suggest that Ca2+ stimulates the breakdown of polyphosphoinositides by stimulating polyphosphoinositide phosphomonoesterase and phosphodiesterase activities in rabbit erythrocyte ghosts. These activities were activated by less than 3 microM Ca2+ in the presence of MgCl2 under hypotonic or isotonic conditions. These Ca2+-stimulated polyphosphoinositide phosphoesterase activities could therefore be active under physiological conditions in normal rabbit erythrocytes.
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D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004910:Erythrocyte Membrane / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D009994:Osmolar Concentration; D010710:Phosphates / Q000097:blood; D010712:Phosphatidic Acids / Q000097:blood; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000097:blood; D010743:Phospholipids / Q000097:blood*; D010744:Phosphoric Monoester Hydrolases / Q000037:antagonists & inhibitors / Q000097:blood*; D010766:Phosphorylation; D011817:Rabbits; D012995:Solubility
D010710:Phosphates; D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010743:Phospholipids; C037178:phosphatidylinositol 4-phosphate; D015636:Magnesium Chloride; D010744:Phosphoric Monoester Hydrolases; D008274:Magnesium; D002118:Calcium