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 c ulture (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 concent ration-dependent increase in accumulation of inositol phosphates in bo th cell types, as assessed by anion exchange chromatography. The effec ts of histamine were most pronounced at 15 to 30 min and were attenuat ed by the H-1-receptor antagonist, pyrilamine. The H-2-receptor antago nist, ranitidine, was without effect. Sodium fluoride (25 mM), a non-r eceptor-associated activator of GTP binding (G) proteins, increased ac cumulation of inositol phosphates within GPTE and PEAS cells. In cells permeabilized with digitonin, the nonhydrolyzable GTP analog, guanosi ne-5'-O-(3-thiotriphosphate) (GTP gamma S; 10 mu M) increased inositol phosphate accumulation. This GTP gamma S-induced increase was attenua ted by exposure to 500 mu M guanosine-5'-O-(2-thiodiphosphate) (GDP be ta S). Additionally, histamine-induced increases in inositol phosphate accumulation were potentiated by GTP gamma S and attenuated by GDP be ta S. These data indicate involvement of a G protein in the response t o histamine. Preincubation with pertussis toxin (100 ng/ml for 4 h) di d not significantly affect the response, suggesting that the associate d G protein was not pertussis toxin-sensitive. The presence of the pho sphatidylinositol-specific phospholipase C (PI-PLC)-associated G prote in, G alpha(q/11), and the presence of mRNA for the Gq family, were as certained by immunoblotting and Northern hybridization, respectively. The results indicate that in airway epithelial cells, histamine, appar ently via an H-1-receptor-mediated process, activates an associated pe rtussis toxin-insensitive G protein(s) (presumably of the Gq family) l inked to PI-PLC, causing hydrolysis of membrane inositol lipids and re sultant accumulation of inositol phosphates within the cells. Activati on of PI-PLC might be involved in a variety of responses of airway epi thelial cells to histamine, such as ion transport and mucin secretion.