PERTUSSIS-TOXIN-SENSITIVE INHIBITION OF GLUCAGON-LIKE PEPTIDE 1-STIMULATED ACID PRODUCTION BY EPIDERMAL GROWTH-FACTOR AND TRANSFORMING GROWTH-FACTOR-ALPHA IN RAT PARIETAL-CELLS

We have recently shown that the intestinal hormone glucagon-like pepti de-1 (GLP-1)-(7-36) amide is a cAMP-dependent stimulant of rat parieta l cell H+ production. Epidermal growth factor (EGF) and transforming g rowth factor-alpha (TGFalpha) are known to inhibit histamine-stimulate d parietal cell function by reducing cAMP production in a pertussis to xin-sensitive manner. Pertussis toxin blocks G(ialpha), the inhibitory subunit of adenylate cyclase, thereby preventing inhibitors from acti ng via G(ialpha). Therefore, we used pertussis toxin as a tool to dete rmine whether EGF and TGFalpha inhibit GLP-1-stimulated parietal cell function via G(ialpha). In enriched (76 +/- 4%) rat parietal cells [C- 14]aminopyrine accumulation and cAMP production were maximally stimula ted by GLP-1-(7-36) amide (10(-8) and 10(-7) M, respectively) or by hi stamine (10(-4) and 10(-3) M, respectively). EGF and TGFalpha (10(-13) -10(-7) M) caused concentration-dependent inhibition of GLP-1-stimulat ed parietal cell function. Maximal inhibition (33% and 37% of the resp onse to GLP-1-(7-36) amide was observed at 10(-8) M EGF and 10(-9) M T GFalpha, respectively. There was a close correlation (r = 0.83; P < 0. 05; n = 71 between the inhibition by EGF and TGFalpha of [C-14]aminopy rine accumulation and the fall in cAMP production in GLP-1-stimulated parietal cells. The identical concentrations of both growth factors wh ich maximally reduced GLP-1-stimulated parietal cell function inhibite d [C-14]aminopyrine accumulation in response to histamine by approxima tely 30%. Thus, the effect of EGF and TGFalpha on the response to GLP- 1 closely resembles that on histamine-induced parietal cell function. Pretreatment with pertussis toxin (300 ng/ml; 37-degrees-C; 4 h) compl etely reversed inhibition by EGF and TGFalpha of aminopyrine accumulat ion and cAMP production following stimulation by either GLP-1 or hista mine. In crude membranes prepared from enriched parietal cells, GLP-1- induced adenylate cyclase activity was inhibited by EGF (10(-8) M) and TGFalpha (10(-9) M) in a pertussis toxin-sensitive manner. We conclud e that EGF and TGFalpha inhibit GLP-1-(7-36)-stimulated parietal cell function via a pertussis toxin-sensitive substrate, presumably G(ialph a), the inhibitory subunit of adenylate cyclase.