Absence of increased electroneutral Na+-H+ exchange in renal cortical brush-border membranes from hyperthyroid rats.
The fluorescence quenching of acridine orange was used to compare Na+-H+ exchange and ion conductances in renal cortical brush-border membrane vesicles (BBMV) isolated from euthyroid and hyperthyroid rats. In BBMV from euthyroid animals, Na+-H+ exchange was entirely electroneutral. In BBMV from hyperthyroid rats, the total rates of Na+-H+ exchange were about 30% higher than in BBMV from euthyroid animals. However, the electroneutral exchange in these membranes was similar to that in BBMV from euthyroid rats; the observed increase in exchange was due to electrically coupled Na+ and H+ movements through conductive pathways in the membranes. Ion conductances in isolated BBMV were tested with outwardly directed K+ gradients in the presence of carbonyl cyanide m-chlorophenylhydrazone (K+ conductance) or valinomycin (H+ conductance). The K+ conductance was negligible and similar in BBMV from both groups of rats. A significant H+ conductance was present in both kinds of membrane preparations and was by 37% higher in BBMV from hyperthyroid animals. Therefore, our experiments failed to demonstrate an increased electroneutral Na+-H+ exchange in BBMV from hyperthyroid rats. Instead, a finding of a significant electrically BBMV from hyperthyroid rats. Instead, a finding of a significant electrically coupled Na+-H+ antiport in the presence of increased H+ conductance in BBMV from hyperthyroid rats indicates that these membranes may also have increased Na+ conductance.
Macković-Basić
M
M
Department of Physiology, Faculty of Medicine, University of Zagreb, Yugoslavia.
Salihagić
A
A
Ries
N
N
Sabolić
I
I
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D006980:Hyperthyroidism / Q000378:metabolism*; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium