Dopaminergic characteristics of isolated parietal cells from rats

Recently we have identified a dopamine-producing system in the gastric mucosa of rats. All the available morphological data suggest that parietal cells synthesize dopamine. In the present study we investigated the dopaminergic characteristics of isolated parietal cells by different methods. Mixed gastric mucosal cells were isolated and size-fractionated by elutriation. The proportion of neurons, parietal and endocrine cells in the fractions were determined by immunocytochemistry (ICC) using antibodies to neurofilament, proton pump and chromogranin A, respectively. No neurons were found in any of the cell preparations, while 56% parietal cell and 0.0% endocrine cell were achieved in the parietally enriched fraction. By Western blot, a tyrosine hydroxylase (TH, the rate-limiting enzyme of the catecholamine synthesis) immunoreactive protein species was demonstrated in isolated mucosal cells, comigrating with the TH immunoreactivity from PC12 cells. The TH immunoreactivity was colocalized to parietal cells by ICC. Dopamine transporter (DAT), a regulator of extracellular/intracellular dopamine balance in the nervous system, was also demonstrated in parietal cells. A significant amount of dopamine and DOPA were measured by HPLC (13.4 and 9.57 pg/10(6) cell, respectively) in parietally enriched cell fraction. Since this enriched cell fraction was virtually clear of both neurons and endocrine cells, demonstration of TH enzyme, DAT and dopamine in this fraction confirms that the parietal cell population might be a major source of dopamine in the rat stomach, supporting our previous results achieved using whole tissue samples.