Amino acid fluxes in rat thin limb segments of Henle’s loop during in vitro microperfusion

Abstract

Amino acids are apparently recycled between loops of Henle and vasa recta in the rat papilla in vivo. To examine more closely papillary amino acid transport, we measured transepithelial fluxes ofl-[14C]alanine and [14C]taurine in thin limbs of Henle’s loops isolated from rat papilla and perfused in vitro. In descending thin limbs (DTL) in vitro, unidirectional bath-to-lumen fluxes tended to exceed unidirectional lumen-to-bath fluxes for both radiolabeled amino acids, although the difference was statistically significant only for taurine. In ascending thin limbs (ATL) in vitro, unidirectional lumen-to-bath fluxes tended to exceed unidirectional bath-to-lumen fluxes, although the difference was again statistically significant only for taurine. These results are compatible with apparent directional movements of amino acids in vivo. However, none of the unidirectional fluxes was saturable or inhibitable, an observation compatible with apparent reabsorption from the ATL in vivo but not compatible with apparent movement from vasa recta to DTL in vivo. There was no evidence of net active transepithelial transport when concentrations of radiolabeled amino acids were matched on both sides of perfused tubule segments. These data suggest that regulation of amino acid movement in vivo may involve the vasa recta, not the DTL of Henle’s loops. The data also suggest that transepithelial movement of amino acids in thin limbs of Henle’s loop may occur via a paracellular route.

Intracellular pH in isolated rat renal papillary thin limbs of Henle's loop

“…1 and 2, the DTL can be readily distinguished from the ATL by the cell structure observed with DIC optics. We are using these segments for studies of amino acid fluxes [7]. So that we might evaluate the possible relationship of pH i to our amino acid flux studies and to our in vivo measurements of vasa recta blood pH [21,26], we measured pH i under buffer conditions similar to those used in our other studies [7].…”

“…All dissections were performed without the aid of enzymatic agents. When possible, we followed individual thin limbs downward from the pars recta of the proximal tubule or from the thick ascending limb [7]. However, such complete dissections were uncommon, and we generally identified DTL and ATL by their distinctive cell types when viewed through an inverted compound microscope with Nomarski differential interference contrast (DIC) optics at 400× magnification [7] (Figs.…”

“…In a previous study on amino acid fluxes [7], we first identified a population of nephrons with both DTL and ATL cell types in the same segment. The regions of DTL-type cells and ATL-type cells varied from a spot region of a few cells of the opposite type to several regional repetitions of alternate cell types to as much as 50% ATL and 50% DTL cell types in a single dissected segment.…”

“…In some experiments, we perfused dissected thin limbs in vitro as described previously [7] using the technique of Burg et al [9] as modified for use in our laboratory [12,13]. Briefly, each tubule Magnification is 400×, as viewed through the microscope was transferred to a special temperature-controlled bathing chamber with a glass bottom.…”

“…There is no change in PCO 2 . Recently, we have been able to isolate papillary thin limbs of Henle's loops without the aid of enzymatic agents from the same strain of rats (Munich Wistar) used in vivo for studies of amino acid transport in vitro [7]. In the course of these studies, we became concerned that the pH of the tubule cells might have an effect on the amino acid transport.…”