Role of nutrient HCO3(-) in protection of amphibian gastric mucosa.
In in vitro bullfrog fundic mucosa inhibited with 10(-3) M metiamide and exposed to a luminal pH of 2 a progressive slow decline in potential difference (PD) and short-circuit current (Isc) and a rise in resistance (R) were observed when the nutrient solution (N) contained 18 mM HCO3(-), but these changes were restored by an N containing 50 mM HCO3(-). Substitution of PO4(3-) or N-tris(hydroxymethyl)-methyl-2-aminoethanesulfonic acid for NHO3(-) in N caused a rapid drop in PD and Isc in inhibited tissues, changes that could be prevented by 10(-4) M histamine. Ulceration occurred more frequently in metiamide-inhibited gastric sacs exposed to artificial gastric juice with an N of 18 mMHCO3(-) than with 50 mM HCO3(-), but histamine prevented ulceration in the 18 mM HCO3(-) solution. JnetCl approximated Isc under most experimental conditions in inhibited mucosa and was reduced dramatically as were both Jn leads to sCl and Js leads to nCl when HCO3(-) was removed from N. In histamine-stimulated tissues, removal of nutrient HCO3(-) did not influence Cl- transport. Our results are consistent with the proposal that HCO3(-) in N supports normal Cl- flux and that the alkaline tide of actively secreting oxyntic cells can do the same in the absence of ambient HCO3(-).
D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism; D005744:Gastric Acid / Q000378:metabolism; D005745:Gastric Acidity Determination; D005753:Gastric Mucosa / Q000187:drug effects*; D006632:Histamine / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D008785:Metiamide / Q000494:pharmacology; D011892:Rana catesbeiana; D013276:Stomach Ulcer / Q000378:metabolism
D001639:Bicarbonates; D002712:Chlorides; D008785:Metiamide; D006632:Histamine