title: Calcium-independent phosphoinositide breakdown in rat basophilic leukemia cells. Evidence for an early rise in inositol 1,4,5-trisphosphate which precedes the rise in other inositol phosphates and in cytoplasmic calcium.
abstract: Aggregation of the receptor with high affinity for immunoglobulin E (IgE) in rat basophilic leukemia cells leads to a calcium-dependent and a calcium-independent hydrolysis of phosphoinositides. The increase in the levels of inositol phosphates induced in the absence of calcium is only 25% of that observed with 1 mM Ca2+. The inositol phosphates reach a new steady state level 2 min after stimulation in EGTA, whereas with calcium they continue to increase up to 15 min. A similar response is observed when the receptors are aggregated due to the interaction of bound IgE with antigen or with anit-IgE, or by the binding of IgE cross-linked chemically. The antigen-mediated response is inhibited by hapten and disruption of such antigen-antibody aggregates late after stimulation leads to a rapid decline in the levels of the inositol phosphates to basal values. Separation of the inositol phosphates by Dowex columns shows that there is a fast rise in inositol trisphosphate which peaks at 15 s and slowly declines to a lower plateau within 2 min. Analysis by high pressure liquid chromatography reveals a 5-fold increase in the levels of inositol 1,4,5-trisphosphate in less than 10 s after stimulation, which precedes any major change in the other inositol phosphates. Aggregation of the receptor in the absence of external calcium induces a transient increase in cytoplasmic calcium which reaches a maximum of approximately 25 nM over basal levels after activation. The onset of the rise in Ca2+ lags after the initial rise in the inositol 1,4,5-trisphosphate.
mesh_terms: D000818:Animals; D001491:Basophils / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D004140:Dinitrophenols / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000097:blood*; D007942:Leukemia, Experimental / Q000097:blood*; D010716:Phosphatidylinositols / Q000097:blood*; D051381:Rats; D011961:Receptors, Fc / Q000378:metabolism; D017455:Receptors, IgE; D011971:Receptors, Immunologic / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000378:metabolism; D013403:Sugar Phosphates / Q000097:blood*
chemical_list: D004140:Dinitrophenols; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D011961:Receptors, Fc; D017455:Receptors, IgE; D011971:Receptors, Immunologic; D013403:Sugar Phosphates; C034638:dinitrophenyl-bovine serum albumin; D012710:Serum Albumin, Bovine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium