HISTAMINE PROVOKES TURNOVER OF INOSITOL PHOSPHOLIPIDS IN GUINEA-PIG AND HUMAN AIRWAY EPITHELIAL-CELLS VIA AN H-1-RECEPTOR G-PROTEIN-DEPENDENT MECHANISM

Guinea pig tracheal epithelial cells in primary air/liquid interface culture (GPTE) and virally transformed human bronchial epithelial cells (BEAS-2B) were exposed to histamine at concentrations of 1 to 100 mu M. At concentrations greater than 1 mu M, histamine elicited a concentration-dependent increase in accumulation of inositol phosphates in both cell types, as assessed by anion exchange chromatography. The effects of histamine were most pronounced at 15 to 30 min and were attenuated by the H-1-receptor antagonist, pyrilamine. The H-2-receptor antagonist, ranitidine, was without effect. Sodium fluoride (25 mM), a non-receptor-associated activator of GTP binding (G) proteins, increased accumulation of inositol phosphates within GPTE and PEAS cells. In cells permeabilized with digitonin, the nonhydrolyzable GTP analog, guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S; 10 mu M) increased inositol phosphate accumulation. This GTP gamma S-induced increase was attenuated by exposure to 500 mu M guanosine-5'-O-(2-thiodiphosphate) (GDP beta S). Additionally, histamine-induced increases in inositol phosphate accumulation were potentiated by GTP gamma S and attenuated by GDP beta S. These data indicate involvement of a G protein in the response to histamine. Preincubation with pertussis toxin (100 ng/ml for 4 h) did not significantly affect the response, suggesting that the associated G protein was not pertussis toxin-sensitive. The presence of the phosphatidylinositol-specific phospholipase C (PI-PLC)-associated G protein, G alpha(q/11), and the presence of mRNA for the Gq family, were ascertained by immunoblotting and Northern hybridization, respectively. The results indicate that in airway epithelial cells, histamine, apparently via an H-1-receptor-mediated process, activates an associated pertussis toxin-insensitive G protein(s) (presumably of the Gq family) linked to PI-PLC, causing hydrolysis of membrane inositol lipids and resultant accumulation of inositol phosphates within the cells. Activation of PI-PLC might be involved in a variety of responses of airway epithelial cells to histamine, such as ion transport and mucin secretion.