Effect of Galactose on Intracellular Potential and Sodium Activity in Urodele Small Intestine. Evidence for Basolateral Electrogenic Transport

Abstract

It has been appreciated for many years that the presence of Na⁺ in the intestinal lumen enhances and indeed is required for active sugar absorption by the small intestinal mucosa. Since the seminal observation (Riklis and Quastel 1958, Czaky and Thale 1960, Crane et al. 1961) was made there have been numerous studies aimed at characterizing the transport mechanism in the brush border. There is now wide acceptance for the view that Na⁺ and sugar are bound and cotransported on the same apical membrane carrier (Fig. la). More recently the way in which sugars are translocated across the basolateral membrane have received attention and these studies, pointing to facilitated diffusion of sugar, are serving to round out our view of transcellular sugar transport and sugar absorption. It has also been known for a long time that actively transported sugars stimulate the absorption of Na⁺ (Fig. lb). For example actively transported sugars increase the transepithelial electrical potential difference (ψ_ms) which is measurable across the wall of the intestine (Barry et al. 1961, Baillien and Schoffeniels 1961, Clarkson et al. 1961, Schachter and Britten 1961). The short-circuit current (I_sc) is similarly stimulated as illustrated in Fig. 2 without any early changes in tissues resistance. Phloridzin, which blocks sugar absorption (Newey et al. 1959) blocks the stimulation of I_sc.