Gastroduodenal HCO3(-) transport: characteristics and proposed role in acidity regulation and mucosal protection.
Gastric HCO3(-) transport (basal) studied in isolated amphibian mucosa and mammalian stomach in vivo amounts to 2-10% of maximal H+ secretion. Duodenal mucosa, devoid of Brunner's glands, transports HCO3(-) at a greater rate (per unit surface area) than either stomach or jejunum in vitro and in vivo. Gastric (but not duodenal) HCO3(-) transport is stimulated by dibutyryl cGMP, carbachol, and cholecystokinin and duodenal (but not gastric) transport by dibutyryl cAMP and gastric inhibitory peptide. Glucagon and E- and F-type prostaglandins stimulate, whereas histamine, gastrin, and secretin are without effect in both stomach and duodenum. Gastric transport very probably occurs by Cl--HCO3(-) exchange at the luminal membranes of the surface epithelial cells. In addition to this mechanism, the duodenum also transports HCO3(-) electrogenically. Lowering the luminal pH increases transport in both the stomach and duodenum. This response, probably mediated via both local production of prostaglandins and tissue-specific humoral agents, may be important in mucosal protection against acid. Metabolism-dependent transport of HCO3(-), stimulated by acid, seems quantitatively sufficient to account for all of the duodenal and most of the gastric mucosa's ability to remove luminal acid.
D000136:Acid-Base Equilibrium; D000818:Animals; D001001:Anura / Q000502:physiology; D001639:Bicarbonates / Q000378:metabolism*; D001693:Biological Transport, Active; D003995:Dibutyryl Cyclic GMP / Q000494:pharmacology; D004068:Digestive System Physiological Phenomena; D004285:Dogs; D004386:Duodenum / Q000378:metabolism; D005744:Gastric Acid; D005753:Gastric Mucosa / Q000378:metabolism* / Q000502:physiology; D006168:Guinea Pigs; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000502:physiology; D007583:Jejunum / Q000378:metabolism
D001639:Bicarbonates; D003995:Dibutyryl Cyclic GMP