The use of potential-sensitive cyanine dye for studying ion-dependent electrogenic renal transport of organic solutes. Spectrophotometric measurements.
ABSTRACT: Renal transport of four different categories of organic solutes, namely sugars, neutral amino acids, monocarboxylic acids and dicarboxylic acids, was studied by using the potential-sensitive dye 3,3'-diethyloxadicarbocyanine iodide in purified luminal-membrane and basolateral-membrane vesicles isolated from rabbit kidney cortex. Valinomycin-induced K(+) diffusion potentials resulted in concomitant changes in dye-membrane-vesicle absorption spectra. Linear relationships were obtained between these changes and depolarization and hyperpolarization of the vesicles. Addition of d-glucose, l-phenylalanine, succinate or l-lactate to luminal-membrane vesicles, in the presence of an extravesicular>intravesicular Na(+) gradient, resulted in rapid transient depolarization. With basolateral-membrane vesicles no electrogenic transport of d-glucose or l-phenylalanine was observed. Spectrophotometric competition studies revealed that d-galactose is electrogenically taken up by the same transport system as that for d-glucose, whereas l-phenylalanine, succinate and l-lactate are transported by different systems in luminal-membrane vesicles. The absorbance changes associated with simultaneous addition of d-glucose and l-phenylalanine were additive. The uptake of these solutes was influenced by the presence of Na(+)-salt anions of different permeabilities in the order: Cl(-)>SO(4) (2-)>gluconate. Addition of valinomycin to K(+)-loaded vesicles enhanced uptake of d-glucose and l-phenylalanine in the presence of an extravesicular>intravesicular Na(+) gradient. Gramicidin or valinomycin plus nigericin diminished/abolished electrogenic solute uptake by Na(+)- or Na(+)+K(+)-loaded vesicles respectively. These results strongly support the presence of Na(+)-dependent renal electrogenic transport of d-glucose, l-phenylalanine, succinate and l-lactate in luminal-membrane vesicles.
PROVIDER: S-EPMC1153971 | BioStudies | 1982-01-01