Effect of in vitro metabolic acidosis on luminal Na+/H+ exchange and basolateral Na+:HCO3- cotransport in rabbit kidney proximal tubules.
The aim of this study was to evaluate the role of the kidney in mediating the signals involved in adaptive changes in luminal Na+/H+ exchange and basolateral Na+:HCO3- cotransport systems in metabolic acidosis. Proximal tubular suspensions were prepared from rabbit kidney cortex and incubated in acidic (A) or control (C) media (pH 6.9 vs 7.4, 5% CO2) for 2 h. Brush border membrane (BBM) and basolateral membrane (BLM) vesicles were isolated from the tubular suspensions and studied for the activity of Na+/H+ exchange and Na+:HCO3- cotransport. Influx of 1 mM 22Na at 10 s (pH6 7.5, pH(i) 6.0) into BBM vesicles was 68% higher in group A compared to group C. The increment in Na+ influx in the group A was amiloride sensitive, suggesting that Na+/H+ exchange was responsible for the observed differences. Kinetic analysis of Na+ influx showed a Km of 8.1 mM in C vs 9.2 in A and Vmax of 31 nmol/mg protein per min in group C vs 57 in A. Influx of 1 mM 22Na at 10 s (pH0 7.5, pH(i) 6.0, 20% CO2, 80% N2) into BLM vesicles was 83% higher in the group A compared to C. The HCO3-dependent increment in 22Na uptake in group A was 4,4'-diisothiocyano-2,2'-stilbene disulfonic acid sensitive, suggesting that Na+:HCO3- cotransport accounted for the observed differences. Kinetic analysis of Na+ influx showed a Km of 11.4 mM in C vs 13.6 in A and Vmax of 35 nmol/mg protein per min in C vs 64 in A. The presence of cyclohexamide during incubation in A medium had no effect on the increments in 22Na uptake in group A. We conclude that the adaptive increase in luminal Na+/H+ exchange and basolateral Na+:HCO3- cotransport systems in metabolic acidosis is acute and mediated via direct signal(s) at the level of renal tubule.
Soleimani
M
M
Department of Medicine, Indiana University School of Medicine, Indianapolis.
Bizal
G L
GL
McKinney
T D
TD
Hattabaugh
Y J
YJ
D000138:Acidosis / Q000378:metabolism*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
D001639:Bicarbonates; D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium