The involvement of cAMP as a second messenger for histamine-induced H+ secretion was studied in a physiologically active, in vitro preparation of piglet gastric mucosa. During the first 5-10 min of stimulation with either histamine or the cAMP phosphodiesterase inhibitor 3-isobutyl-1,4-methylxanthine (IBMX), increases (≥5-fold) in tissue cAMP content ([cAMP]) were well correlated with the characteristic decrease in transepithelial resistance (R); these changes precede H+ secretion by several minutes. Control experiments indicate that, during these treatments, tissue [cAMP] is dominated by the [cAMP] of oxyntic cells alone; changes in R and H+ are also related to activity of these cells alone. At the steady state (45 min), histamine and IBMX caused equivalent increases in H+ and decreases in R, but [cAMP] was markedly different in the two cases. With IBMX [cAMP] was elevated at least fivefold, whereas with histamine [cAMP] was ≤50% above resting levels. The tissue is also stimulated by exogenous additions of dibutyryl cAMP. A histamine-sensitive adenylate cyclase was present in isolated, purified oxyntic cells. The histamine sensitivity of the cyclase was very similar to that which the intact tissue exhibits for histamine-induced changes in H+ and R. The cyclase activity was blocked by cimetidine but not by promethazine. We concluded that during stimulation histamine activates a histamine (H2)-sensitive adenylate cyclase of oxyntic cells, and there is a rapid increase in cellular [cAMP] that is involved in activation of H+ transport and other associated changes of oxyntic cells. An active phosphodiesterase is responsible for reducing [cAMP] to a level much below the 'peak' value. Other cellular factors (e.g., protein kinases and Ca2+ calmodulin) must also be involved in the maintenance of the stimulated state of oxyntic cells.
|Original language||English (US)|
|Journal||American Journal of Physiology - Gastrointestinal and Liver Physiology|
|Publication status||Published - 1982|
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