Interactions of external and internal K+ with K(+)-HCO3- cotransporter of rat medullary thick ascending limb
| Autor: | René-Alexandre Podevin, M. Paillard, Anne Blanchard, Maurice Bichara, Françoise Leviel |
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| Rok vydání: | 1996 |
| Předmět: |
Male
inorganic chemicals Absorption (pharmacology) animal structures Nigericin Physiology Potassium Analytical chemistry chemistry.chemical_element Medullary interstitium digestive system Michaelis–Menten kinetics Rats Sprague-Dawley chemistry.chemical_compound Extracellular Animals Ion transporter Kidney Medulla urogenital system Sodium-Bicarbonate Symporters Osmolar Concentration Cell Biology Hydrogen-Ion Concentration Rats Bicarbonates Kinetics Biochemistry chemistry Loop of Henle Carrier Proteins Cotransporter |
| Zdroj: | American Journal of Physiology-Cell Physiology. 271:C218-C225 |
| ISSN: | 1522-1563 0363-6143 |
| Popis: | We studied [K + ] i and [K + ] o , where subscripts i and o refer to intracellular and extracellular, respectively, concentration dependency of the kinetic properties of the electroneutral K + -HCO 3 - cotransport, using suspensions of rat medullary thick ascending limb (mTAL). With the use of nigericin and monensin, [K + ] i was clamped at various values, while maintaining [Na + ] i = [Na + ] o = 37 mM, [HCO 3 - ] i = [HCO 3 - ] o = 23 mM, and pH i = pH o = 7.4. As indicated by 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein HCO 3 - -dependent rates of change in pH i , at constant [K + ] i , increasing the magnitude of the outward K + gradient by varying [K + ] o saturated HCO 3 - efflux with a Michaelis-Menten curve (apparent Michaelis constant for [K + ] o = 2 mM, Hill coefficient = 1). On the other hand, increasing [K + ] i from 30 to 140 mM, while either [K + ] o or the magnitude of the K + concentration gradient was fixed, saturated HCO 3 - efflux with a sigmoidal curve and yielded a Hill coefficient of 3.4 and 50% of maximum velocity at 70 mM [K + ] i . These results indicate that [K + ] i , independent of its role as a transportable substrate for the cotransport with HCO 3 - , has a role as an allosteric activator of the K + -HCO 3 - cotransporter. Such an allosteric modulation may contribute to the maintenance of net HCO 3 - absorption despite large in vivo physiological variations of K + concentration in the medullary interstitium. |
| Databáze: | OpenAIRE |
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