The conventional short-circuiting technique under-short-circuits most epithelia

Abstract

The relationships among ion current, membrane potential difference, and resistance of an epithelium are studied. The short-circuit technique introduced by Ussing and Zerahn does not completely short circuit the epithelium if the series resistance parallel to the cell layer between the voltage electrodes is not properly compensated. The residual potential difference across the epithelial cell layer in the "short-circuit state" is proportional to both the measured short-circuited small intestinal mucosa the villus and crypt areas are hypo-polarized to different degrees rather than simultaneously hyper- and hypo-polarized. Short-circuiting the whole tissue reduces but does not abolish the passive net ion movement across the tissue. Measurements of the electrical properties of the whole and denuded rat distal small intestine in HCO3-Ringer solution containing 10 mM glucose reveal that the measured short-circuit current has under-estimated approximately 33% of the true short-circuit current and that the passive net Na flux from serosa to mucosa and Cl flux from mucosa to serosa are not negligible in the "short circuit state."

Mechanisms of diarrhea in the interleukin-2-deficient mouse model of colonic inflammation

“…This correction, applied to bath resistance, is well accepted, but it is also necessary to correct I sc and net fluxes for the R sub of intestinal preparations. The implications of this correction have previously been provided (15,22,47,48,51). Generally, after correction for the bathing solution, the true active transport rate becomes underestimated by a factor that is given by the ratio of R t and R e .…”

K + Secretion in Rat Distal Jejunum

“…This should be noticeable in a correlation between the unidirectional fluxes and the short-circuit current, as a residual transepithelial potential depends directly on I sc [42]. Therefore, all control fluxes were plotted against the I sc measured during the respective period (Fig.…”

Adaptation of Epithelial Ion Transport in the Short Bowel Syndrome

“…To compare epithelial ion transport in intestine undergoing adaptation, the epithelial/subepithelial resistance ratio is needed to correct Isc [5], Thus, measuring voltage divider ratios after positioning the tip of a microelectrode just below the epithelium al lowed us to determine epithelial and subepi thelial resistance and subsequently to quan tify electrolyte transport of the mucosa in the short bowel syndrome by means of the Ussing technique.…”

“…For comparing transport data of control and short bowel it is necessary to correct for the respective subepithelial resistance con tributions [5], After correcting for the bath resistance, the factor by which the measured transport rate underestimates the true active transport is given by the ratio of total wall resistance over epithelial resistance [2,5,7,9] which is the reciprocal of the voltage divider ratios given above or shown in ta ble 1. Correction factors were 1.78 ± 0.09 (n = 48) for the control ileum and 2.36 ± 0.08 (n = 67; p < 0.001) for the short bowel.…”

“…The solution was gassed with a mixture of 95% Oi and 5% COi and had a pH of 7.4 at 37 °C. All 1«; values were corrected for the resistance o f the bathing medium as described by Tai and Tai [5], Glucose-dependent electrogenic Na absorption was measured in a medium containing 48 mM 3-o-methyl-glucose, a hexose absorbed by the glucose carrier, but not metabolized by the intestine [6]. The decrease in 1* (Alsc) after addition of phlori zin (0.5 mM) to the mucosal side of the Ussing cham ber was considered equivalent to glucose-dependent Na absorption.…”