Angiotensin II Enhances Connecting Tubule Glomerular Feedback

Abstract

Increasing Na delivery to epithelial Na channels (ENaCs) in the connecting tubule (CNT) causes dilation of the afferent arteriole (Af-Art), a process we call CNT glomerular feedback (CTGF). Angiotensin II (Ang II) stimulates ENaC in the collecting duct via Ang II type 1 receptors. We hypothesized that Ang II in the CNT lumen enhances CTGF by activation of Ang II type 1 receptors, protein kinase C and ENaC. Rabbit afferent arterioles and their adherent CNT were microperfused and preconstricted with norepinephrine. Each experiment involved generating 2 consecutive concentration-response curves by increasing NaCl in the CNT lumen. During the control period, the maximum dilation of the afferent arteriole was 7.9±0.4 μm, and the concentration of NaCl in the CNT needed to achieve half maximal response (EC 50 ) was 34.7±5.2 mmol/L. After adding Ang II (10 −9 mol/L) to the CNT lumen, the maximal response was 9.5±0.7 μm and the EC 50 was 11.6±1.3 mmol/L ( P =0.01 versus control). Losartan, an Ang II type 1 antagonist (10 −6 mol/L) blocked the stimulatory effect of Ang II; PD123319, an Ang II type 2 antagonist (10 −6 mol/L), did not. The protein kinase C inhibitor staurosporine (10 −8 mol/L) added to the CNT inhibited the stimulatory effect of Ang II. The ENaC inhibitor benzamil (10 −6 mol/L) prevented both CTGF and its stimulation by Ang II. We concluded that Ang II in the CNT lumen enhances CTGF via activation of Ang II type 1 and that this effect requires activation of protein kinase C and ENaC. Potentiation of CTGF by Ang II could help preserve glomerular filtration rate in the presence of renal vasoconstriction.