On the mechanism of stimulation of H+ transport in gastric mucosa by Ca++ ionophore A23187. I. Pathways for cytosolic calcium increase.
The pathways for cytosolic Ca++ increase under A23187 stimulation of H+ secretion were studied in the isolated gastric mucosa of the toad Bufo marinus. A23187 produced a more potent stimulation of secretion when added to the mucosal side which did not contain calcium. Measurements of ionophore incorporation by fluorometric methods indicated that A23187 incorporates into oxyntic cells intracellularly. The presence of divalent cations inhibited incorporation. This may be the reason for a more potent action when A23187 was added from the mucosal side. Withdrawal of calcium from serosal solution largely inhibited the secretory response to A23187 added to the mucosal side. Reintroduction of calcium into the serosal side in the presence of ionophore elicited H+ secretion. The results are consistent with an uptake of A23187 from the mucosal side into cellular organelles and basolateral membranes. Calcium entry through the serosal side may be responsible for triggering secretion. Although A23187 likely releases calcium from intracellular stores, its rate of release may not be sufficient to bring about a full stimulation of secretion in serosal-Ca++-free conditions.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002024:Bufo marinus; D000001:Calcimycin / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D005744:Gastric Acid / Q000378:metabolism; D005753:Gastric Mucosa / Q000187:drug effects / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D066298:In Vitro Techniques; D010295:Parietal Cells, Gastric / Q000187:drug effects / Q000378:metabolism; D013268:Stimulation, Chemical
D000001:Calcimycin; D006859:Hydrogen; D002118:Calcium