Chloride uptake by brush border membrane vesicles isolated from rabbit renal cortex. Coupling to proton gradients and
Abstract:
Brush border membrane vesicles were isolated from rabbit renal cortex by Mg(++)-precipitation and differential centrifugation. (36)Cl(-) and [(3)H]glucose uptakes were simultaneously determined by a rapid filtration technique. Lysis of the vesicles with distilled water abolished 90-95% of the radioactivity on the filters, suggesting that nearly all of the (36)Cl(-) and [(3)H]glucose counts represented uptake into an osmotically reactive intravesicular space. Inwardly directed K(+) gradients plus valinomycin stimulated (36)Cl(-) uptake, demonstrating a conductive pathway for chloride uptake into brush-border membrane vesicles. (36)Cl(-) uptake could also be stimulated by inwardly directed proton gradients (pH(outside) < pH(inside)). This effect was seen in the absence of sodium, as well as in the presence of valinomycin when the vesicles had equal K(+) concentrations inside and out. An "overshoot" phenomenon was observed when external (36)Cl(-) was 2 mM and the external pH was lowered from 7.5 to 6.0 or to 4.5. The effect of the proton gradient was presumed to be different from the conductive mechanism because (a) the stimulation of (36)Cl(-) uptake by inwardly directed K(+) diffusion potentials was additive to the proton gradient effect, and (b) competition studies revealed statistically significant effects of thiocyanate on the conductive pathway, but not on the proton-driven pathway.HCl cotransport or anion exchange are electrically neutral mechanisms which could couple (36)Cl(-) uptake to inwardly-directed proton gradients in a brush border membrane vesicle. If both electrically neutral and conductive path ways for chloride transport are present in the luminal membrane of the proximal tubule, then the mechanism as well as the direction of net chloride transport will be influenced by the nature of the accompanying cation transport process.
Related Concept Videos
Reabsorption and Secretion in the PCT
Transport mechanisms involving sodium ions (Na+) contribute significantly to solute reabsorption. These mechanisms include symport and antiport processes.
A key example is the...
Reabsorption and Secretion in the Loop of Henle
Reabsorption and Secretion in the DCT and Collecting Duct
The distal part of the DCT, along with the...
Formation of Concentrated Urine
Pore Transport and Ion-Pair Transport
Pore transport, also known as convective transport, is a process where small molecules like urea, water, and sugars rapidly cross cell membranes as though there were channels or pores in the membrane. Although direct microscopic evidence is limited but the concept of pores or channels is widely accepted based on physiological evidence. Despite the lack of direct microscopic...
Physiology of the Genitourinary System II: Tubular Reabsorption and Secretion


