Angiotensin II stimulates calcium and nitric oxide release from Macula densa cells through AT1 receptors

A fluorescent nitric oxide (NO) indicator, 4,5-diaminofluorescein diacetate, and the calcium indicator, indo-1, with 488 nm and 364 nm UV confocal laser scanning microscopy were used to detect NO and calcium concentration in rabbit macula densa (MD) cells challenged by angiotensin II (Ang II). Glomeruli with attached thick ascending limbs with the MD plaque were isolated and perfused. Ang II concentration from 10(-9) to 10(-5) progressively increased MD cell calcium and NO to peak values at 10(-6) and 10(-7), respectively. Ang II (10(-6) M) caused the cytosolic calcium concentration (Ca(2+)](i)) to increase by 125.8+/-16.3 nM (n=17) from the bath and by 52.3+/-11.5 nM (n=18) from the lumen. AT(1) antagonist CV-11974 (10(-6) M) blocked the Ang II-induced calcium responses from bath and lumen, but AT(2) antagonist PD-123319 (10(-6) M) did not. AT(2) agonist CGP-42112A (10(-6) M) did not affect Ca(2+)](i) in MD cells from either side. Ang II (10(-6) M) increased the NO production by 16%+/-3.4% (n=26) from the bath and by 18%+/-3.1% (n=24) from the lumen. CV-11974 (10(-6) M) blocked the NO responses from both sides, but PD-123319 (10(-6) M) did not on either side. CGP-42112A (10(-6) M) had no effect on NO in MD cells. In calcium-free experiments there was no difference from the result in normal calcium solutions. In conclusion, we found that Ang II increased Ca(2+)](i) and stimulated NO production in MD cells from the basolateral and luminal sides through AT(1) receptors.