title: Potassium depletion increases luminal Na+/H+ exchange and basolateral Na+:CO3=:HCO3- cotransport in rat renal cortex.
abstract: Most HCO3- reabsorption in proximal tubules occurs via electroneutral Na+/H+ exchange in brush border membranes (BBMS) and electrogenic Na+:CO3=:HCO3- cotransport in basolateral membranes (BLMS). Since potassium depletion (KD) increases HCO3- reabsorption in proximal tubules, we evaluated these transport systems using BBM and BLM vesicles, respectively, from control (C) and KD rats. Feeding rats a potassium deficient diet for 3-4 wk resulted in lower plasma [K+] (2.94 mEq/liter, KD vs. 4.47 C), and higher arterial pH (7.51 KD vs. 7.39 C). KD rats gained less weight than C but had higher renal cortical weight. Influx of 1 mM 22Na+ at 5 s (pHo 7.5, pHi 6.0, 10% CO2, 90% N2) into BLM vesicles was 44% higher in the KD group compared to C with no difference in equilibrium uptake. The increment in Na+ influx in the KD group was DIDS sensitive, suggesting that Na+:CO3=:HCO3- cotransport accounted for the observed differences. Kinetic analysis of Na+ influx showed a Km of 8.2 mM in KD vs. 7.6 mM in C and Vmax of 278 nmol/min/mg protein in KD vs. 177 nmol/min/mg protein in C. Influx of 1 mM 22Na+ at 5 s (pHo 7.5, pHi 6.0) into BBM vesicles was 34% higher in the KD group compared to C with no difference in equilibrium uptake. The increment in Na+ influx in the KD group was amiloride sensitive, suggesting that Na+/H+ exchange was responsible for the observed differences. Kinetic analysis of Na+ influx showed a Km of 6.2 mM in KD vs. 7.1 mM in C and Vmax of 209 nmol/min/mg protein in KD vs. 144 nmol/min/mg protein in C. Uptakes of Na(+)-dependent [3H]glucose into BBM and [14C]succinate into BLM vesicles were not different in KD and C groups, suggesting that the Na+/H+ exchanger and Na+:CO3=:HCO3- cotransporter activities were specifically altered in KD. We conclude that adaptive increases in basolateral Na+:CO3=:HCO3- cotransport and luminal Na+H+ exchange are likely responsible for increased HCO3- reabsorption in proximal tubules of KD animals.
authors.affiliation: Department of Medicine, Indiana University Medical Center, Indianapolis.
authors.forename: M
authors.initials: M
authors.lastname: Soleimani
authors.forename: J A
authors.initials: JA
authors.lastname: Bergman
authors.forename: M A
authors.initials: MA
authors.lastname: Hosford
authors.forename: T D
authors.initials: TD
authors.lastname: McKinney
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D001692:Biological Transport; D002254:Carbonates / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007672:Kidney Cortex / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000502:physiology*; D011522:Protons; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D002254:Carbonates; D011522:Protons; D012964:Sodium; D011188:Potassium