Effects of Ca2+ ions on gastric acid secretion by the rat isolated stomach.
The role of Ca2+ in the stimulatory action of histamine has been evaluated in the isolated gastric fundus from immature rats, by changing the concentration of calcium ions in the bathing solutions. Lowering Ca2+ to 1.2 mM greatly enhanced the secretory response to histamine, while leaving unaffected that to the H2-receptor agonist, dimaprit. The effect of histamine was competitively antagonized by ranitidine (pA2 = 6.78) in normal solutions; conversely in 1.2 mM Ca2+, the antagonism by ranitidine became unsurmountable. Basal rates of acid secretion did not change in low Ca2+ solutions, whereas they were reduced approximately by 50% in Ca2+-free media. Finally, the secretory response to theophylline was significantly lower in low Ca2+ solutions in comparison with that in control conditions. From the above results it may be concluded that changes in the concentration of Ca2+ ions caused different changes in the secretory response of the rat stomach in the various experimental conditions. The marked enhancement of the response to histamine observed in low Ca2+ is unlikely to be connected with H2-receptors, as suggested by the lack of interference in the response to dimaprit, but it could be related to intracellular mechanisms (H+/K+-ATPase, carbonic anhydrase activation etc.).
D000262:Adenylyl Cyclases / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000502:physiology*; D017259:Dimaprit; D004305:Dose-Response Relationship, Drug; D005744:Gastric Acid / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D051381:Rats; D011968:Receptors, Histamine / Q000502:physiology; D013806:Theophylline / Q000494:pharmacology; D013890:Thiourea / Q000494:pharmacology
D011968:Receptors, Histamine; D006632:Histamine; D013806:Theophylline; D000262:Adenylyl Cyclases; D013890:Thiourea; D002118:Calcium; D017259:Dimaprit