Adenosine receptors on canine parietal cells modulate gastric acid secretion to histamine

Administration of theophylline has been shown to enhance gastric acid secretion in humans. Because theophylline has been reported to be a poor inhibitor of phosphodiesterase but a better adenosine receptor antagonist, we tested the hypothesis that there are inhibitory "R site" adenosine receptors on parietal cells. Utilizing isolated dispersed canine parietal cells, we measured acid secretion by the [14C]aminopyrine accumulation technique. We tested the effect of increasing concentrations of 2-chloroadenosine (10(-7), 10(-6), 10(-5) M) and L-N6-phenylisopropyl adenosine (L-PIA) (10(-7), 10(-6), and 10(-5) M), stable analogs of adenosine with specificity for the R sites, on aminopyrine uptake produced by submaximal stimulating concentrations of histamine (1 microM) plus isobutyl methylxanthine (3 microM) or carbachol (1 microM). Histamine-stimulated parietal cell aminopyrine uptake was 4.3- +/- 0.4-fold above basal; 2-chloroadenosine inhibited this response in a dose-dependent fashion with a 57 +/- 6% inhibition at 10(-5) M.L-PIA also inhibited histamine-stimulated aminopyrine uptake with a 67 +/- 11% inhibition at 10(-5) M. Carbachol-stimulated aminopyrine uptake was 5.8- +/- 1.6-fold above basal, but 2-chloroadenosine had no significant effect on this response. Theophylline, 300 microM, and 8-phenyltheophylline, 10 microM, reduced the inhibitory effect of 2-chloroadenosine. 8-Phenyltheophylline was inactive in inhibiting the parietal cell phosphodiesterase activity and the IC50 of theophylline for phosphodiesterase was 1 mM. Because prostaglandins inhibit parietal cell uptake of aminopyrine in a pattern similar to 2-chloroadenosine, we also tested the possibility that prostaglandins are involved in the 2-chloroadenosine response.(ABSTRACT TRUNCATED AT 250 WORDS)