Studies of acid and alkaline secretion by rabbit gastric fundus in vitro: effect of low concentrations of sodium taurocholate.

The effect of low concentrations of sodium taurocholate on the secretory and electrical activity of isolated rabbit fundic mucosa has been studied. Fundic mucosa maintained a stable potential difference (10.2 +/- 0.6 mV, n = 70) and electrical resistance (85 +/- 6 omega . cm-2, n = 70) and the majority of preparations spontaneously secreted acid (2.85 +/- 0.31 mumol . cm-2 . h-1, n = 70). Histamine (10(-5) and 10(-4) M) and carbachol (10-4 M) increased acid secretion, and these responses were prevented by cimetidine (10(-3) M) and atropine (10(-5) M), respectively. Mucosal application of taurocholate (10(-4) and 10(-3) M) increased net acidity without altering electrical activity. This response exhibited tachyphylaxis, was not altered by pretreating the tissues with cimetidine (10(-3) M), atropine (10(-5) M), or somatostatin (10(-6) M), and occurred in mucosas maximally stimulated by histamine. Sodium thiocyanate (6 x 10(-2) M, serosal side) inhibited spontaneous acid secretion revealing net alkalinization (0.83 +/- 0.05 mumol . cm-2 . h-1, n = 58) that was completely inhibited by anoxia and potassium cyanide (10(-2) M) and markedly reduced by 2,4-dinitrophenol (10(-4) M). Some fundic preparations spontaneously secreted alkali (1.20 +/- 0.20 mumol . cm-2 . h-1, n = 6) after an initial period of acid secretion. Mucosal-side taurocholate (10(-3) M) converted net alkali secretion by both thiocyanate-treated and spontaneously-secreting mucosas to acid secretion without affecting electrical conductance. These secretory responses may be implicated in the pathogenesis of gastric mucosal damage by bile salts.