metiamide and thiocyanate

Inhibitors of the initial step (H2-antagonist) and of the final step (thiocyanate, SCN-; and nitrite, NO2-) were used to study the dynamics of acid secretion in isolated frog gastric mucosa. Tissues were mounted in flow-through chambers, and the acid secretion rate (SR) was recorded on a pH-stat microprocessor. Continuous presence of H2-antagonist decreases the SR to a lower steady state, and on removal the SR returns to basal SR, causing a net loss of acid, the nonconservative effect. The amount of lost acid is a unique function of exposure, thus, independent of the patterns (pulses or steps) of inhibition. In contrast, continuous presence of SCN- or NO2- (below 3 mM) results in an undershoot in SR with a return to basal SR, whereas at higher concentrations there is no return. Removal of these inhibitors causes an overshoot in SR with return to basal SR. The rebound acid is equal to acid suppressed by NO2- and low concentration of SCN-, resulting in no net loss of acid, the conservative effect, whereas at high concentrations of SCN- there is an apparent loss of acid. In maximally secreting tissue the overshoot of SR is not observed. However, the acid is not lost, merely delayed. In resting tissue NO2- also merely delays the exit of the acid produced in response to forskolin. The rebound acid is proposed to reside in a sequestered "acid" pool that is stable for at least 120 min. Results with NO2- and SCN- suggest an effect on a saturable exit enzyme, possibly the K+-H+-ATPase.

Topics: Animals; Gastric Acid; Histamine; In Vitro Techniques; Metiamide; Nitrites; Rana catesbeiana; Stimulation, Chemical; Thiocyanates; Thiourea