GASTRIN AND CARBACHOL REQUIRE CAMP TO ELICIT AMINOPYRINE ACCUMULATIONIN ISOLATED PIG AND RAT PARIETAL-CELLS

The role of endogenous adenosine 3',5'-cyclic monophosphate (cAMP) in the mechanisms of action of gastrin and carbachol on aminopyrine accum ulation in isolated pig and rat parietal cells was investigated. In pi g cells, pentagastrin (100 nM) alone stimulated aminopyrine accumulati on, an action significantly reduced by the protein kinase A inhibitor Rp-adenosine 3',5'-cyclic monophosphothioate (Rp-cAMP[S]; 100 mu M), I n rat cells, gastrin-17 (100 nM) was incapable of stimulating aminopyr ine accumulation, but it potentiated the action of histamine (100 mu M ). Carbachol (10 mu M) stimulated aminopyrine accumulation and potenti ated the action of histamine, and its action was potentiated in a dose -dependent manner by Sp-adenosine 3',5'-cyclic monophosphothioate (Sp- cAMP[S]; a cAMP analogue) in both species. The effect of carbachol was dose dependently reduced by Rp-cAMP[S]. The basal cAMP in pig parieta l cells was 3.5-fold higher than that in rat parietal cells. Histamine (100 mu M) and 3-isobutyl-1-methylxanthine (IBMX; 100 mu M) only slig htly elevated the cAMP content (1.2- to 2.9-fold the basal level) in b oth pig and rat parietal cells. Their combination, however, increased the cAMP level by 8- to 38-fold, but it did not increase aminopyrine a ccumulation above that elicited by histamine alone. Gastrin did not al ter the cAMP levels in parietal cells of either of the two species. Bo th gastrin and carbachol increased cytosolic free Ca2+ in enriched pig and rat parietal cells. These results indicated that in isolated pig and rat parietal cells 1) secretagogues that elevate intracellular fre e Ca2+, such as gastrin and carbachol, require a certain cAMP level to be effective in stimulating aminopyrine accumulation; 2) a further in crease over a certain level of cAMP does not result in an increased am inopyrine accumulation; and 3) parallel activation of Ca2+- and cAMP-d ependent pathways appears to be necessary to effectively elicit aminop yrine accumulation.