Localization of Gastrin Receptors in Intact Isolated and Separated Rat Fundic Cells

Previous studies have suggested the presence of "high affinity" receptor sites (K = 0.60 to 0.80 10–8 m) for gastrin (3H-labeled G17-I) in purified plasma membranes from rat fundic mucosa (FEBS Lett 66:168-172, 1976). The present study deals with the cellular localization of these receptor sites. Dispersed rat fundic cells were prepared by pronase dissociation. Populations of 10 to 70% "large cells" (i.e., parietal cells) were obtained by successive 100 × g 45-sec centrifugations. Of the cells, 93 ± 5% excluded trypan blue; oxygen consumption ranged from 3.5 (10% large cells) to 15 nmoles O2 min–1 per 106 cells (70% large cells); cell ultrastructural integrity was very well preserved. 3H-Labeled G17- I binding to isolated cells was temperature-dependent, proportional to cell concentration, reversible, and a saturable process as a function of time and hormone concentration. Association and dissociation rate constants were k1 = 0.69 × 107 m–1 min–1 and k–1 = 0.063 min–1, respectively, at 20°C, pH 7.4. In the range of the study, a Scatchard plot of the binding was suggestive of a single class of binding sites with an equilibrium constant K = 0.90 × 10–8 m and a maximum binding capacity of 7500 sites per cell (crude suspension). Binding increased linearly as a function of the enrichment in parietal cells, the theoretical maximum binding capacity (100% parietal cell population) being 14,000 to 19,000 sites per cell. These findings on intact fundic cells compare favorably with those previously found on their derived plasma membranes. It is therefore suggested that, in the rat, parietal cells contain the high affinity gastrin receptors.