Measurement of [14C]aminopyrine accumulation in isolated parietal cells

Investigation of gastroprotective compounds at subcellular level in isolated gastric mucosal cells

We tested the hypothesis that recognized gastroprotective agents exert direct protection against ethanol-induced injury in isolated rat gastric mucosal cells in vitro. If protection exists, we also wanted to identify subcellular targets in the reversible and/or irreversible stages of cell injury. Ethanol-induced cell injury was quantified by measuring plasma membrane leakage (trypan blue exclusion and lactate dehydrogenase release), mitochondrial integrity (succinic dehydrogenase), and nuclear damage (ethidium bromide-DNA fluorescence). Initial cell viability and responsiveness were estimated by the effects of carbachol, carbachol + atropine, or 16,16-dimethyl-PGE(2) on chief cell pepsinogen secretion. Enriched parietal cells were stimulated by histamine, carbachol, or histamine + IBMX. Preincubation of cells with PG, sucrose octasulfate, or the sulfhydryl compounds N-acetylcysteine, taurine, or cysteamine increased cell resistance </=21% against ethanol. Similar protection was found with low histamine concentrations, but a higher concentration aggravated ethanol toxicity. Other naturally occurring or synthetic gastroprotective agents offered partial protection or aggravated ethanol-induced cell injury. Only a few in vivo gastroprotective agents demonstrated in vitro direct cytoprotection, which involved mainly the reversible stage of cell injury (e.g., plasma membrane changes) and, less often, irreversible (e.g., mitochondrial and nuclear) damage. Our findings also indicate that a major part of the beneficial effect of gastroprotective agents is expressed at the tissue level.

Gastric prostaglandin E2 receptors are the common antisecretory target of mucosal prostanoids

The gastric mucosa produces all principal prostaglandin (PG) types, but receptor binding studies in this tissue have as yet been performed exclusively with [3H]PGE2. Therefore we compared the binding of different 3H-labelled prostanoids to fundic mucosal plasma membranes from the porcine stomach. Binding sites for [3H]PGE2, [3H]iloprost and [3H]PGF2 alpha had similar nanomolar dissociation constants with high affinities for unlabelled PGE2. Iloprost and PGF2 alpha were 10- and 100-fold less potent competitors with Hill slopes near unity in all cases. In further [3H]PGE2 competition studies the affinities of prostanoid ligands with selectivity for different PG receptor types correlated closely with their respective antisecretory potencies, as tested by [14C]aminopyrine uptake in isolated porcine parietal cells. We conclude that parietal cell PGE2 receptors are the common antisecretory target for all prostanoid types in the porcine stomach. There was no evidence for other mucosal PG receptors possibly involved in acid secretion.