The cytosolic chloride concentration in macula densa and cortical thick ascending limb cells

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Abstract
It is believed that chloride transport through the macula densa (MD) cells is a factor involved in the tubuloglomerular feedback (TGF) mechanism and in MD-mediated renin release. In this study isolated and perfused rabbit kidney cortical thick ascending limb (cTAL) segments containing MD plaques and attached glomeruli were loaded with chloride (CL-sensitive) 6 methoxy-1-fluorophore (sulphanate-propyl) quinolinium (SPQ). MD and cTAL intracellular chloride concentration ([Cl-]i) was determined by using image-intensified video microscopy and digital image-processing for measuring the intensity of the emitted SPQ fluorescence. With 150 mM NaCl in lumen and bath the [Cl-]i in MD and cTAL cells was 58.8 +/- 7.2 mM (n = 20) and 68.7 +/- 9.8 mM (n = 14), respectively. When the presumed luminal Na(+)-2Cl(-)-K+ co-transporter was blocked by adding 10(-4)M furosemide, the [Cl-]i was reduced in both, MD and cTAL cells from 55.5 +/- 11.9 to 28.6 +/- 10.0 mM (n = 10) and from 43.8 +/- 2.6 to 13.1 +/- 4.5 mM (n = 5), respectively. A reduction in luminal NaCl from 150 to 30 mM also decreased both, MD and cTAL [Cl-]i from 69.4 +/- 9.1 to 36.5 +/- 5.1 mM (n = 9) and from 82.9 +/- 14.5 to 49.4 +/- 8.0 mM (n = 8), respectively. Basolateral addition of the Cl(-)-channel blocker NPPB increased MD [Cl-]i from 31.1 +/- 2.0 to 100.7 +/- 17.0 mM (n = 5) and cTAL [Cl-]i from 44.4 +/- 12.9 to 89.7 +/- 11.7 mM (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)