Gastrin stimulation of histamine synthesis in enterochromaffin-like cells from rabbit fundic mucosa

Abstract

This work aimed to investigate the molecular role of gastrin in histamine synthesis in isolated rabbit fundic mucosal cells enriched in enterochromaffin-like (ECL) cells (37%). Gastrin stimulated histidine decarboxylase (HDC) activity by increasing the maximal velocity (Vmax) from 0.240 +/- 0.017 (basal value) to 0.332 +/- 0.012 pmol/mg protein/h and by decreasing the Michaelis-Menten constant value -Km; 73.90 +/- 2.2 vs. 93.42 +/- 4.32 microM (basal value)]. Pertussis toxin (PTX) (200 ng/ml) reduced the stimulation of HDC induced by 10 nM gastrin from 41.8 to 15.9%, whereas cholera toxin (CTX) (100 ng/ml) was without effect. Staurosporine and polymyxin B inhibited in a dose dependent manner the HDC activity stimulated by 10 nM gastrin. Phorbol 12-myristate 13-acetate (PMA; 100 nM) decreased Vmax (0.558 +/- 0.021 pmol/ mg protein/h) but did not change the Km. Furthermore, cycloheximide (0.1-10 microM) inhibited the gastrin-induced stimulation of HDC activity, whereas actinomycin D (up to 10 microM) was without effect. Finally, incubation of cells with gastrin (10 microM) left the expression of HDC mRNA unchanged. We concluded that gastrin, acting through "gastrin/CCK-B type" receptors coupled to PTX-sensitive G protein, exerts a short-term regulation of histamine synthesis in gastric ECL cells by increasing both the affinity of HDC for L-histidine and the number of active enzyme molecules. This last event, related to protein kinase C activation, could be due to a translational or posttranslational mechanism.