Effect of nonhydrolyzable guanosine phosphate on IgE-mediated activation of phospholipase C and histamine release from rodent mast cells

Rat mast cells and bone marrow-derived mouse mast cells (BMMC) were sensitized with mouse IgE mAb, and permeabilized by ATP to introduce guanosine-5'-O-(3-thiotriphosphate) (GTPγS) and/or guanosine-5'-O-(2-thiodiphosphate) (GDPβS) into the cells. After ATP-induced lesions were resealed with Mg²⁺, the cells were challenged by Ag to determine the effect of the nonhydrolyzable guanosine phosphate on Ag-induced hydrolysis of phosphoinositides and histamine release. Introduction of GTPγS into permeabilized rat mast cells or BMMC, followed by exposure of the cells to extracellular Ca²⁺, resulted in histamine release, but failed to induce hydrolysis of phosphoinositides. It was also found that introduction of GTPγS into the cells did not synergistically enhance Ag-induced histamine release. Introduction of GDPβS into sensitized BMMC inhibited the GTPγS-dependent, Ca²⁺-induced histamine release but failed to inhibit Ag-induced histamine release. The results suggest that GTPγS-dependent, Ca²⁺-induced histamine release and Ag-induced histamine release go through independent biochemical pathways. It was also found that introduction of GTPγS or GDPβS into sensitized BMMC neither enhanced nor inhibited Ag-induced formation of inositol phosphates. These results together with previous findings that pretreatment of BMMC with either pertussis toxin or cholera toxin does not affect Ag-induced hydrolysis or phosphoinositides, indicate that a G protein is involved in the transduction of IgE-mediated triggering signals to phospholipase C in rodent mast cells.