Adaptation of epithelial ion transport in the short bowel syndrome

Ileal remnants 8 weeks after 70% proximal small intestinal resection were used as a model for the short bowel syndrome in man. For comparing active ion transport between control ileum and short bowel with the Ussing technique, the relative contribution of the subepithelial resistance has to be considered. Epithelial/subepithelial voltage divider ratios were determined in the Ussing chamber by positioning the tip of a microelectrode just below the epithelium. In control ileum, the ratio of total to epithelial voltage deflection was 1:0.56 +/- 0.03 (n = 48) and decreased to 1:0.42 +/- 0.01 (n = 67; p less than 0.001) under the short bowel condition. Thus, the factors by which a measured short-circuit current (Isc) underestimates the true electrogenic transport was 1.78 +/- 0.09 (n = 48) in control ileum and 2.36 +/- 0.08 (n = 67; p less than 0.001) in the short bowel. Glucose-dependent electrogenic Na absorption was defined using bathing media containing 48 mM 3-o-methyl-glucose as the decrease in Isc (delta Isc) after addition of 0.5 mM phlorizin. After correction for the respective contributions of the subepithelial resistance, delta Isc was -1.4 +/- 0.2 microEq.h-1.cm-2 (n = 13) in control ileum and -3.2 +/- 0.7 microEq.h-1.cm-2 (n = 11; p less than 0.01) in the short bowel. We conclude that the mucosa in the short bowel syndrome is characterized by an increase in glucose-dependent electrogenic Na absorption, probably as an adaptive response to the reduced overall absorptive area of the remaining intestine.