Effects of cations and pH on apical membrane potential of in vitro Necturus antrum

Abstract

The surface epithelial cells of the gastric mucosa transport Na+ from lumen to serosa. The first step in this process is the entry of Na+ through an amiloride-sensitive Na+ channel at the apical membrane. The exact function(s) of this Na+ transport are unknown, but it has been suggested that it might help the stomach to withstand an acid load. The present study was undertaken to examine the effects of low luminal pH and the alkali cations Li+, K+, Rb+, and Cs+ on the amiloride-sensitive Na+ permeability of the apical membrane of Necturus antral cells by measuring the changes in apical membrane voltage (Vmc) using conventional microelectrode techniques. Isosmolar replacement of luminal NaCl (pH 7.25) with LiCl caused a depolarization of the Vmc, a decrease in transepithelial resistance (Rt), and an increase in the transepithelial potential (Vmc), whereas replacement with KCl, RbCl, or CsCl caused a hyperpolarization of the Vmc, an increase in Rt, and a decrease in the Vmc. Luminal acidification from pH 7.25 to pH 3.00 caused very similar changes with all the cation solutions tested, hyperpolarizing the Vmc, increasing Rt, and reducing the Vmc to near 0 mV. Acidification of the luminal NaCl solution from pH 7.25 to pH 2.00 caused a progressive hyperpolarization of the Vmc similar to the effects seen with luminal amiloride (10(-4) M) in pH 7.25 NaCl solutions or luminal Na+-free (N-methyl-D-glucamine) Ringer at pH 7.25. These results demonstrate that 1) of the cations tested only Li+ can substitute for Na+ in maintaining the Vmc, and 2) external H ions (low luminal pH) block cation permeability of the apical membrane.

Use of commercially available cell culture inserts for primary culture and electrophysiologic studies of guinea pig gastric mucous epithelial cells

“…The measurement of electrical potentials and resistances on the gastric mucous cell monolayers were performed according to previously described techniques (28,55,58,69). The transepithelial potential (V,~) was measured with a high impedance electrometer (FD223, WPI) by means of Ag/AgC1 electrodes connected to both bathing solutions through 3,5% agar-Ringer bridges with the serosal solution grounded.…”

“…The 1~ was calculated from R t = AVe/I, where AV~ equals the transepithelial voltage deflection, and I equals the transepithelial current density. The ratio "a" of membrane resistances RJRb (Ra, apical membrane resistance, R b, basolateral membrane resistance) was calculated as previously described (28,55,58,69). All monolayer resistances were corrected for the resistance of the filter and solutions.…”

Protection of the Gastrointestinal Tract Epithelium against Damage from Low pH Beverages

“…Similar to the esophageal epithelia, gastric mucosal cells have a low permeability to hydrogen and other ions due to the hydrophobicity of the membrane and the presence of tight junctions between the cells at the apical surface (Hills and others 1983; Machen and Paradiso 1987; Silverthorn and others 1998). Furthermore, it has been demonstrated that apical membrane resistance increases in gastric surface cells in response to luminal acid (Rutten and others 1989; Mustonen and Kivilaakso 1997). Decreased paracellular permeability also has been observed following exposure to acid in 1 study (Takezono and others 2004); however, a transient increase was reported in a 2nd study (Phillipson and others 2003).…”