Superoxide enhances Na-K-2Cl cotransporter activity in the thick ascending limb
| Autor: | Ramiro Juncos, Jeffrey L. Garvin |
|---|---|
| Rok vydání: | 2005 |
| Předmět: |
Male
chemistry.chemical_classification Reactive oxygen species Sodium-Potassium-Chloride Symporters Physiology Reabsorption Superoxide Sodium Cell Polarity Rats Enzyme Activation Rats Sprague-Dawley chemistry.chemical_compound Cotransporter activity chemistry Biochemistry Superoxides Loop of Henle Biophysics Animals Na+/K+-ATPase Cotransporter Na absorption Solute Carrier Family 12 Member 1 K channels |
| Zdroj: | American Journal of Physiology-Renal Physiology. 288:F982-F987 |
| ISSN: | 1522-1466 1931-857X |
| DOI: | 10.1152/ajprenal.00348.2004 |
| Popis: | Superoxide (O2−) enhances Na reabsorption by the thick ascending limb (THAL). Na absorption in this segment involves the Na-K-2Cl cotransporter, K channel, and Na-K-ATPase. We hypothesized that O2−stimulates NaCl absorption primarily by enhancing Na-K-2Cl cotransport. First, we measured steady-state intracellular Na (Nai) and chloride (Cli). Xanthine oxidase (XO; 0.75 mU/ml) and hypoxanthine (HX; 0.125 mM) were added to the bath to increase O2−. During the control period, Naiwas 12.2 ± 1.9 mM. After treatment with O2−, it rose to 20.9 ± 3.3 mM, a 71% increase ( P < 0.01). Clialso increased ( P < 0.01). Neither XO nor HX alone had a significant effect on Naior Cli. Next, we tested cotransport activity by measuring the initial rate of increase in Naicaused by changing luminal Na-Cl-K from 50/0/0 to 140/134/4 mM. During the control period, the initial rate of increase was 0.13 ± 0.02 arbitrary units (AU)/min. After treatment with O2−, it was 0.22 ± 0.04 AU/min ( P < 0.025), a 69% increase. Neither XO nor HX alone had a significant effect. Furosemide completely blocked the increase in intracellular Na in the control and O2−treatment periods. Next, we studied K channel activity by measuring the depolarization caused by increasing luminal K from 1 to 25 mM using a voltage-sensitive dye. During the control period, maximum depolarization was 7.31 ± 0.77 AU. After O2−treatment, it was 6.18 ± 0.90 AU ( P < 0.05), a 15% decrease. Finally, we assessed the effects of O2−on Na-K-ATPase activity in THAL suspensions by measuring ATP hydrolysis. Vmaxand K1/2for Na were not affected by O2−. We concluded that O2−stimulates THAL NaCl absorption primarily by enhancing Na entry via Na-K-2Cl cotransport. |
| Databáze: | OpenAIRE |
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