Effect of secretagogues and barium ion on resting frog stomach

Stimulation of acid secretion in a resting stomach is normally associated with a decrease in transmucosal resistance. An increase in permeability to an ion may accordingly play a crucial role in the action of secretagogues. Stimulation may thus entail increased entry of K⁺, an ion known to be essential for acid secretion. In support of this argument are the findings that removal of K⁺ from the nutrient solution elevated resistance and drastically impaired the secretory response to added acetylcholine and histamine. Ba⁺⁺ is known to decrease the K⁺ conductance of the nutrient facing membranes of the stomach, so its effects should resemble those induced by K⁺ removal. It was found that addition of 5mM Ba⁺⁺ to the nutrient solution bathing resting mucosae first decreased and later increased resistance over initial values. In the same group of experiments (n=16), Ba⁺⁺ increased acid secretion from 1.9 ± 0.12 to 5.5 ± 0.53 μEq/h per 2.85 cm² of mucosa. Subsequent responses to histamine and acetylcholine were diminished by Ba⁺⁺ pretreatment. In the absence of nutrient K⁺, both the increase in resistance and the stimulation of acid secretion due to Ba⁺⁺ were markedly reduced. Thus in the concentration used here, Ba⁺⁺ appears to exert effects not explained by restriction of K⁺ entry.