Glucose inhibits insulin release when not promoting the entry of calcium into the beta-cells

The effect of antigen on the metabolism of polyphosphoinositides was investigated in sensitized rat peritoneal mast cells. Addition of antigen to rat peritoneal mast cells prelabelled with 3H]arachidonic acid resulted in a very rapid decrease in the level of phosphatidylinositol 4-phosphate (DPI) within 5 sec, which appeared to precede the breakdown of phosphatidylinositol (PI), while there was no significant decline of PI 4,5-bisphosphate (TPI). The reduced levels of these phosphoinositides returned almost to control or even slightly higher values by 300 sec in parallel with the antigen-stimulated 32P]phosphate incorporation into these lipids. This early and transient disappearance in DPI prior to that in PI was also observed in 3H]glycerol-prelabelled cells. These data suggest that DPI degradation upon stimulation by antigen in mast cells may be an initial step in the histamine release process.