Kinetics of sodium‐dependent solute transport by rabbit renal and jejunal brush‐border vesicles using a fluorescent dye.

Abstract

SUMMARY1. The kinetics of Na-coupled solute transport by renal and jejunal brush-border vesicles in the rabbit were examined using the potential-sensitive fluorescent dye diS-C3-(5).2. All organic solutes known to be transported across these membranes by Na-coupled mechanisms increase the fluorescence of the dye in the presence of Na, but not K. An increase in fluorescence (AF) corresponds to a depolarization of the electrical potential difference (5-60 mV) across the brush-border membrane in the intact cell. AF was independent of the valency of the transported solute.3. The fluorescence response was saturable, and for twelve solutes the K,, i.e. the concentration of the substrate generating 50 % of the maximal response, agreed quite closely with the Kt values reported from tracer studies.4. For six solutes increasing the Na concentration decreased K,, and this agrees with the effect of Na on the kinetics of succinate transport in renal vesicles.5. We conclude that D-glucose, neutral amino acids and imino acids are co-transported with Na across both renal and jejunal brush-border membranes, and that carboxylic acids, fl-amino acids, and dibasic amino acids are co-transported with Na across the renal, but not jejunal, membranes.

Electrophysiology of succinate transport across rabbit renal brush border membranes.

“…The succinate potential is saturable and the apparent Km is comparable to that found for tracer succinate uptake (see Schell et al 1983). Furthermore, the succinate Km increases with decreasing Na+ concentration in both dye and tracer experiments without changes in the maximal rates (Schell et al 1983;Wright, Hirayama, Kaunitz, Kippen & Wright, 1983).…”

“…The succinate potential is saturable and the apparent Km is comparable to that found for tracer succinate uptake (see Schell et al 1983). Furthermore, the succinate Km increases with decreasing Na+ concentration in both dye and tracer experiments without changes in the maximal rates (Schell et al 1983;Wright, Hirayama, Kaunitz, Kippen & Wright, 1983). These observations, along with the Na+ specificity of succinate uptake (Wright et al 1982) point to an intrinsic relation between Na+/succinate co-transport and the succinate potential.…”

“…All experiments were carried out at 22°C, and all other methods are as described previously (Schell et al 1983).…”

“…Membrane potentials in vesicle suspensions were measured as described previously (Schell et al 1983) except that the optical response of the dye was also recorded in the absorbance mode as described by Salama, Johnson & Scarpa (1980). An Aminco DW-2UV/VIS dual wave-length spectrometer was used to measure the difference in absorbance between 655 and 685 nm.…”

Effects of Amphotericin B on Renal Transport

“…The activity of membrane transport was observed using the potential sensitive dye 3,3-dipropylthiadicarbocyanine iodide [1]. Because Na + -dependent transport systems are electrogenic, their activity can be observed as changes in membrane potential, which, in turn, are proportional to the observed fluorescence response of the dye [2], In the absence of amphotericin B, the kinetics of N a+-dependent transport was observed and demonstra ted classical saturable response ( fig.…”