Angiotensin II Stimulates Renin in Inner Medullary Collecting Duct Cells via Protein Kinase C and Independent of Epithelial Sodium Channel and Mineralocorticoid Receptor Activity

Abstract

Collecting duct (CD) renin is stimulated by angiotensin (Ang) II, providing a pathway for Ang I generation and further conversion to Ang II. Ang II stimulates the epithelial sodium channel via the Ang II type 1 receptor and increases mineralocorticoid receptor activity attributed to increased aldosterone release. Our objective was to determine whether CD renin augmentation is mediated directly by Ang II type 1 receptor or via the epithelial sodium channel and mineralocorticoid receptor. In vivo studies examined the effects of epithelial sodium channel blockade (amiloride; 5 mg/kg per day) on CD renin expression and urinary renin content in Ang II–infused rats (80 ng/min, 2 weeks). Ang II infusion increased systolic blood pressure, medullary renin mRNA, urinary renin content, and intrarenal Ang II levels. Amiloride cotreatment did not alter these responses despite a reduction in the rate of progression of systolic blood pressure. In primary cultures of inner medullary CD cells, renin mRNA and (pro)renin protein levels increased with Ang II (100 nmol/L), and candesartan (Ang II type 1 receptor antagonist) prevented this effect. Aldosterone (10 −10 to 10 −7 mol/L) with or without amiloride did not modify the upregulation of renin mRNA in Ang II–treated cells. However, inhibition of protein kinase C with calphostin C prevented the Ang II–mediated increases in renin mRNA and (pro)renin protein levels. Furthermore, protein kinase C activation with phorbol 12-myristate 13-acetate increased renin expression to the same extent as Ang II. These data indicate that an Ang II type 1 receptor–mediated increase in CD renin is induced directly by Ang II via the protein kinase C pathway and that this regulation is independent of mineralocorticoid receptor activation or epithelial sodium channel activity.