ANG II controls Na⁺-K⁺( NH 4 + )-2Cl⁻cotransport via 20-HETE and PKC in medullary thick ascending limb

Cell pH was monitored in medullary thick ascending limbs to determine effects of ANG II on Na⁺-K⁺(${NH}_4^{+}$ )-2Cl⁻cotransport. ANG II at 10⁻¹⁶to 10⁻¹² M inhibited 30–50% (P < 0.005), but higher ANG II concentrations were stimulatory compared with the 10⁻¹² M ANG II level cotransport activity; eventually, 10⁻⁶ M ANG II stimulated 34% cotransport activity (P < 0.003). Inhibition by 10⁻¹²M ANG II was abolished by phospholipase C (PLC), diacylglycerol lipase, or cytochrome P-450-dependent monooxygenase blockade; 10⁻¹² M ANG II had no effect additive to inhibition by 20-hydroxyeicosatetranoic acid (20-HETE). Stimulation by 10⁻⁶ M ANG II was abolished by PLC and protein kinase C (PKC) blockade and was partially suppressed when the rise in cytosolic Ca²⁺ was prevented. All ANG II effects were abolished by DUP-753 (losartan) but not by PD-123319. Thus ≤10⁻¹² M ANG II inhibits via 20-HETE, whereas ≥5 × 10⁻¹¹ M ANG II stimulates via PKC Na⁺-K⁺(${NH}_4^{+}$ )-2Cl⁻cotransport; all ANG II effects involve AT₁ receptors and PLC activation.