Chloride-Dependent Intracellular pH Regulation via Extracellular Calcium-Sensing Receptor in the Medullary Thick Ascending Limb of the Mouse Kidney
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The extracellular calcium-sensing receptor (CaSR) located in either luminal or basolateral cell membranes of various types of renal tubules including proximal tubules, Henle's loop and collecting ducts has been thought to play a fundamental role in electrolyte metabolism. To further identify the physiological roles of the CaSR, we examined the effects of Ca<sup>2+</sup> and calcimimetics neomycin (Neo), gentamicin and gadolinium chloride (Gd<sup>3+</sup>) on the intracellular pH (pHi) of in vitro microperfused mouse medullary thick ascending limb (mTAL) cells of Henle's loop, by loading the cells with fluorescent pH indicator 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein and measuring the ratio of fluorescence emission at 530 nm after exciting the dye at 490 and 440 nm. In a steady-state condition in Hepes-buffered solution, the pHi in the mTALs was 7.29 ± 0.04 (<i>n</i> = 9). A concentration of 200 μmol/l Neo in the basolateral side decreased the pHi after 1 min by −0.13 ± 0.02 (<i>n</i> = 34, <i>p</i> < 0.0001). The other calcimimetics showed similar effects on pHi, whereas none of these calcimimetics in the lumen affected pHi. Na<sup>+</sup> removal or the inhibition of Na<sup>+</sup> and proton transport with amiloride, bumetanide, or bafilomycin did not eliminate the effect of Neo on pHi. On the other hand, Cl<sup>−</sup> removal clearly eliminated the Neo-induced pHi decrease (−0.06 ± 0.01 vs −0.00 ± 0.05 in Cl<sup>−</sup> removal, <i>n</i> = 4, <i>p</i> < 0.003). Thus, we have demonstrated for the first time that the CaSR is involved in the regulation of the pHi in the mTAL and requires Cl<sup>−</sup> to exert its effect.
- Tohoku J. Exp. Med.
Tohoku J. Exp. Med. 210(4), 291-300, 2006-12-01
Tohoku University Medical Press