Angiotensin II directly stimulates macula densa Na-2Cl-K cotransport via apical A[T.sub.1] receptors

Angiotensin II directly stimulates macula densa Na-2Cl-K cotransport via apical A[T.sub.1] receptors. Am J Physiol Renal Physiol 282: F301-F306, 2002. First published October 23, 2001; 10.1152/ajprenal.00129. 2001.--ANG II is a modulator of tubuloglomerular feedback (TGF); however, the site of its action remains unknown. Macula densa (MD) cells sense changes in luminal NaCl concentration ([[NaCl].sub.L]) via a Na-2Cl-K cotransporter, and these cells do possess ANG II receptors. We tested whether ANG II regulates Na-2Cl-K cotransport in MD cells. MD cell [Na.sup.+] concentration ([[[Na.sup.+]].sub.i]) was measured using sodium-binding benzofuran isophthalate with fluorescence microscopy. Resting [[[Na.sup.+]].sub.i] in MD cells was 27.7 [+ or -] 1.05 mM (n = 138) and increased ([DELTA][[[Na.sup.+]].sub.i]) by 18.5 [+ or -] 1.14 mM (n = 17) at an initial rate ([DELTA][[[Na.sup.+]].sub.i]/[DELTA]t) of 5.54 [+ or -] 0.53 x [10.sup.-4] U/s with an increase in [[NaCl].sub.L] from 25 to 150 mM. Both [DELTA][[[Na.sup.+]].sub.i] and [DELTA][[[Na.sup.+]].sub.i]/[DELTA]t were inhibited by 80% with 100 [micro]M luminal furosemide. ANG II ([10.sup.-9] or [10.sup.-12 M]) added to the lumen increased MD resting [[[Na.sup.+]].sub.i] and [[NaCl].sub.L]-dependent [DELTA][[[Na.sup.+]].sub.i] and caused a twofold increase in [DELTA][[[Na.sup.+]].sub.i]/[DELTA]t. Bath ([10.sup.-9] M) ANG II also stimulated cotransport activity, and there was no additive effect of simultaneous addition of ANG II to bath and lumen. The effects of luminal ANG II were furosemide sensitive and abolished by the A[T.sub.1] receptor blocker candesartan. ANG II at [10.sup.-6] M failed to stimulate the cotransporter, whereas increased cotransport activity could be restored by blocking A[T.sub.2] receptors with PD-123, 319. Thus ANG II may modulate TGF responses via alterations in MD Na-2Cl-K cotransport activity. furosemide; tubuloglomerular feedback; angiotensin receptor blockade; cytosolic sodium concentration; fluorescent microscopy