Possible Interaction: Phosphatidylinositol 4,5-Diphosphate and Calcium Supplement

“Model membrane studies have shown that PIP2 can form electrostatic-based clusters with Ca++ and with basic peptides.”

“Incubation of erythrocytes with [32P]phosphate resulted in a linear incorporation of the label into PtdIns(4,5)P2 (phosphatidylinositol 4,5-…), and PA (phosphatidic acid) over a period of 2 h at 37 degrees C. Exposure of 32P-labelled erythrocyte ghosts to calcium caused … PtdIns(4,5)P2 ….”

“Actin filament-depolymerizing agents (cytochalasins and desoxyribonuclease I) accelerated channel rundown, while actin filament stabilizer (phalloidin) or phosphatidylinositol biphosphate PIP2 ; inhibitor of F-actin-severing proteins) inhibited spontaneous and/or Ca2+ -induced rundown.”

“In cellular homogenates prepared in the presence of EGTA and stored at 4 degrees , readdition of calcium resulted in a time-dependent increase in inositol 1,4,5-trisphosphate mass and a decrease in the mass of phosphatidylinositol 4,5-bisphosphate (PIP(2)).”

“In the Ca++-insensitive or activated R cilia, PIP2 levels are intermediate, increasing only marginally with increased [ Ca++].”

“The Ca2+ -induced channel modification was prevented partially by phosphatidylinositol 4,5-bisphosphate (PIP2) and completely by ATP and PIP2 together, but not by ATP alone.”

“The rate of Ca2+ release induced by PIP2 was approximately greater than 50% slower than the rates induced by other agents (e.g. caffeine, Ca2+ , ATP).”

“Incubation of the membrane fraction of anterior pituitary homogenate with [3H]inositol-labeled PIP2 in the presence of calcium increased the concentration of the water-soluble degradation product inositol trisphosphate (IP3) in a time-dependent manner.”

“From these measurements it can be estimated that, in the presence of GTP gamma S and calcium buffered to 130 nM, hydrolysis of PIP2 accounts for at least 10 times as much diacylglycerol as direct PI breakdown despite the 100-fold excess of PI over PIP2.”

“Although the relationship between the hydrolysis of PtdIns(4,5)P2 and the mobilization of intracellular calcium was clearly demonstrated, the direct link between Ins(1,4,5)P3 production and the physiological response was only implied.”