Chloride concentration in macula densa and cortical thick ascending limb cells

The Cl- transport through the macula densa (MD) cells is believed to be a link in the tubuloglomerular feedback (TGF) believed to be a link in the tubuloglomerular feedback (TGF) mechanism and MD-mediated renin release. One step in this transport is probably the electroneutral and furosemide-sensitive Na(+)-K(+)-2Cl- contransport on the luminal membrane of MD cells. Another step is transport through basolateral Cl- channels. In the present study the intracellular Cl- concentration, [Cl-]i, was measured in the MD and cortical thick ascending limb (cTAL) cells, and the concentration changes elicited by blocking the Na(+)-K(+)-2Cl- cotransport with furosemide or by lowering the luminal NaCl concentration determined. We also investigated the effects of blocking the basolateral Cl- channels. A preparation consisting of a segment of the cTAL, MD cells, and the attached glomerulus was dissected from rabbit kidneys. The preparation was loaded with the Cl(-)-sensitive fluorophore SPQ, and perfused by using the isolated and perfused tubule technique. The intracellular chloride concentration was determined with a video system using digital imaging that measured the intensity of the emitted SPQ fluorescence. The T 1/2 of the leakage of SPQ was found to be (197 +/- 60) min (n = 9). With 150 mM NaCl in the lumen and bath, [Cl-]i in MD cells was 47 +/- 13 mM (n = 8) and 54 +/- 13 mM (n = 5) in cTAL cells. When furosemide (10(-4) M) was added to the luminal perfusion, the MD cell [Cl-]i was reduced to 6 +/- 2 mM. The corresponding value in cTAL cells was 5 +/- 3 mM.(ABSTRACT TRUNCATED AT 250 WORDS)