Interpretation of hexose-dependent electrical potential differences in small intestine.

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ACTIVELY transported sugars added to the solution bathing the mucosal surface of the small intestine produce an increase in the electrical potential difference (p.d.) and short-circuit current (Isc) across the tissue1–4. Schultz and Zalusky1 have shown that the increase in the Isc (ΔIsc) across rabbit ileum is a function of both sugar and sodium concentrations in the bathing solution. When sodium was replaced with potassium, the maximum ΔIsc caused by addition of sugars was a linear function of sodium concentration. Recently, Barry et al.5 reported that the increase in the p.d. (Δp.d.) following addition of galactose to the mucosal bathing solution of everted sacs of rat mid-intestine is independent of sodium concentration when mannitol is used to replace sodium chloride, but is approximately a linear function of sodium concentration when potassium is used to replace sodium. They have concluded that the “galactose dependent potential is unaffected by sodium concentration but is reduced by increasing potassium concentration”. Lyon and Crane6 have reported that, in rat jejunum, the maximum Δp.d. resulting from addition of actively transported sugars is independent of sodium concentration when tris [2-amino-2(hydroxymethyl)-1,3-propanediol] is used to replace sodium, but decreases when potassium is used as replacement ion.