Effects of Amiloride on the in Vitro Frog Gastric Mucosa

Abstract

Amiloride, a pyrazine diuretic, has been shown to decrease the secretion of K+ by the renal tubule (1-3). Although this effect has been explained as a result of the inhibitory aation of the drug on Na+ reabsorption, the possibility exists that amiloride might directly affect K+ permeability. This thought led to the speculation that amiloride might likewise affect the K+ permeability of the frog gastric mucosa which lends itself well to such an investigation. From the literature (4, S ) , it appears that the K+ resistance of the nutrient membrane of frog gastric mucosa is about half the C1-resistance and that other ionic resistances are very high relative to the K+ and C1-resistances.Since K + has been found to be essential for HCl secretion (6), perhaps if amiloride affected the K+ permeability it might also decrease the H+ secretory rate. Experiments were, therefore, designed to test the effect of arniloride on the transmembrane resistance, the transmembrane potential difference (PD), and the H-+ secretory rate in high and low nutrient K + -solutions.Methods. The experiments were performed on gastric mucosae of Rana pipiens with an in vitro method described in detail elsewhere ( 7 ) . In this method each mucosa was mounted between cylindrical chambers. Two pairs of electmodes were used, one for sending current across the mucosla and the other for measuring the PD. The resistance was determined as the change in PD per unit of applied current. The nutrient bathing solution contained ( m u ) : Na+, 101; K+, 4; Ca2+, 1; Mg2+, 0.8; C1-, 81; HC03-, 25; phosphate, 1.0; and glucose, 10; and the secretory bathing solution: Na+, 102; K+, 4; C1-, 106. In high K+ nutrient solutions, K+ replaced Na+, B~t h sides of the mucosa were gassed with 95% O2 and 5% C02.The pH of the secretory solution was maintained at 4.90. After the control part of the experiment, amiloride was added in the nutrient solution to a 0.5 or 2.0 mM concentra tion.Results. Figure 1 shows the effects of adding amiloride to the nutrient solution. At the time indicated by the arrow, amiloride was added to a concentration of 0.5 mM in the nutrient solution. A comparison was generally made of the changes in the parameters in about 30 min following the addition of amilorirde in the nutrient solution to the control values just before the addition. As shown in Fig. 1, the resistance inlcreased about SO%, the PD decreased about 15%, and the H+ rate decreased about 30%. Washing both sides of the mucosa with regular solutions produced only a partial recovery of the parameters towards control values. In about 40% of the experiments after washing with regular solutions, the resistance decreased to some extent towards control values while the H+ rate persisted at about the same level as with amiloride in the nutrient solution. Table I sulmmarizes the main results. Columns 111, V and VII give, respectively, the average resistances, PD and H+ rates of mucosae bathed in regular solutions without amiloride. Columns IV, VI and VIII give, respectively, the average percentag...

Effects of -Adrenergic Amines on Frog Gastric Mucosa

“…The pH of the secretory side was maintained at 4.90. The nutrient bathing solution contained (in mMj: Na+, 102; K+, 4; Ca2+, 1; Mg2+, 0.8; 81; 25; phosphate, 1 .O; and glucose,10; and the secretory bathing solution contained: Na+, 102; K+, 4; C1-, 106. Both sides of the mucosa were gassed with 95% O2 and 5% CO,.…”

“…On the other hand, agents or procedures which increase the resistance of ionic pathways on the nutrient membrane are usually associated with small decreases in the H+ secretory rate (9,10). Rose et al (4) provided an analysis based on these facts to explain changes in PD arising from changes in resistance.…”

“…The interpretation here is complicated by the fact that the relative magnitudes of Elcl and E, are not well established. If one assumes that E'cl > E, (10).…”

Effects of Norepinephrine and Phentolamine on Frog Gastric Mucosa in Chloride Solutions

“…Agents or procedures which markedly increase the resistance of the H+and/or Cl--active pumps on the secretory membrane produce a concurrent marked decrease in the H+ secretory rate (6,7). On the other hand, agents or procedures which increase the resistance of the ionic pathways on the nutrient membrane are usually asssociated with small decreases in the H+ secretory rate (8,9).…”

“…[l] and [3] one may deduce that a decrease in PDNS should result if only R& increases, while an increase in PDNS would be observed if only RK increases (9). Dividing numerator and denominator of the fraction in the middle of Eq.…”