Na+,K+-ATPase is modulated by angiotensin II in diabetic rat kidney--another reason for diabetic nephropathy?
ABSTRACT Angiotensin II (ANGII) plays a central role in the enhanced sodium reabsorption in early type 1 diabetes in man and in streptozotocin-induced (STZ) diabetic rats. This study investigates the effect of untreated STZ-diabetes leading to diabetic nephropathy in combination with ANGII treatment, on the abundance and localization of the renal Na(+),K(+)-ATPase (NKA), a major contributor of renal sodium handling. After 7 weeks of STZ-diabetes (i.v. 65 mg kg(-1)) a subgroup of control (C) and diabetic (D7) Wistar rats were treated with ANGII (s.c. minipump 33 microg kg(-1) h(-1) for 24 h; CA and D7A). We measured renal function and mRNA expression, protein level, Serin23 phosphorylation, subcellular distribution, and enzyme activity of NKA alpha-1 subunit in the kidney cortex. Diabetes increased serum creatinine and urea nitrogen levels (C versus D7), as did ANGII (C versus CA, D7 versus D7A). Both diabetes (C versus D7) and ANGII increased NKA alpha-1 protein level and enzyme activity (C versus CA, D7 versus D7A). Furthermore, the combination led to an additive increase (D7 versus D7A, CA versus D7A). NKA alpha-1 Ser23 phosphorylation was higher both in D7 and ANGII-treated rats in the non-cytoskeletal fraction, while no signal was detected in the cytoskeletal fraction. Control kidneys showed NKA alpha-1 immunopositivity on the basolateral membrane of proximal tubular cells, while both D7 and ANGII broadened NKA immunopositivity towards the cytoplasm. Our study demonstrates that diabetes mellitus (DM) increases the mRNA expression, protein level, Ser23 phosphorylation and enzyme activity of renal NKA, which is further elevated by ANGII. Despite an increase in total NKA quantity in diabetic nephropathy, the redistribution to the cystosol suggests the Na(+) pump is no longer functional. ANGII also caused translocation from the basolateral membrane, thus in diabetic states where ANGII level is acutely elevated, the loss of NKA will be exacerbated. This provides another mechanism by which ANGII blockade is likely to be protective.
Article: Intracellular Na+ regulates dopamine and angiotensin II receptors availability at the plasma membrane and their cellular responses in renal epithelia.[show abstract] [hide abstract]
ABSTRACT: The balance and cross-talk between natruretic and antinatruretic hormone receptors plays a critical role in the regulation of renal Na+ homeostasis, which is a major determinant of blood pressure. Dopamine and angiotensin II have antagonistic effects on renal Na+ and water excretion, which involves regulation of the Na+,K+-ATPase activity. Herein we demonstrate that angiotensin II (Ang II) stimulation of AT1 receptors in proximal tubule cells induces the recruitment of Na+,K+-ATPase molecules to the plasmalemma, in a process mediated by protein kinase Cbeta and interaction of the Na+,K+-ATPase with adaptor protein 1. Ang II stimulation led to phosphorylation of the alpha subunit Ser-11 and Ser-18 residues, and substitution of these amino acids with alanine residues completely abolished the Ang II-induced stimulation of Na+,K+-ATPase-mediated Rb+ transport. Thus, for Ang II-dependent stimulation of Na+,K+-ATPase activity, phosphorylation of these serine residues is essential and may constitute a triggering signal for recruitment of Na+,K+-ATPase molecules to the plasma membrane. When cells were treated simultaneously with saturating concentrations of dopamine and Ang II, either activation or inhibition of the Na+,K+-ATPase activity was produced dependent on the intracellular Na+ concentration, which was varied in a very narrow physiological range (9-19 mm). A small increase in intracellular Na+ concentrations induces the recruitment of D1 receptors to the plasma membrane and a reduction in plasma membrane AT1 receptors. Thus, one or more proteins may act as an intracellular Na+ concentration sensor and play a major regulatory role on the effect of hormones that regulate proximal tubule Na+ reabsorption.Journal of Biological Chemistry 09/2003; 278(31):28719-26. · 4.77 Impact Factor
Article: ANG II enhances contractile responses via PI3-kinase p110 delta pathway in aortas from diabetic rats with systemic hyperinsulinemia.[show abstract] [hide abstract]
ABSTRACT: We investigated the involvement of ANG II and phosphatidylinositol 3-kinase (PI3-K) in the enhanced aortic contractile responses induced by hyperinsulinemia in chronic insulin-treated Type 1 diabetic rats. Plasma ANG II levels were elevated in untreated compared with control diabetic rats and further increased in insulin-treated diabetic rats. Aortic contractile responses and systolic blood pressure were significantly enhanced in chronic insulin-treated diabetic rats compared with the other groups. These insulin-induced increases were largely prevented by cotreatment with losartan (an ANG II type 1 receptor antagonist) or enalapril (an angiotensin-converting enzyme inhibitor). LY-294002 (a PI3-K inhibitor) diminished the increases in contractile responses in ANG II-incubated aortas and aortas from chronic insulin-treated diabetic rats. The norepinephrine (NE)-stimulated levels of p110 delta-associated PI3-K activity and p110 delta protein expression were increased in aortas from insulin-treated diabetic compared with control and untreated diabetic rats, and chronic administration of losartan blunted these increases. Contractions were significantly larger in aortas from diabetic rats incubated with a low concentration (inducing approximately 10% of the maximum contraction) of ANG II or with NE or isotonic K+ than in aortas from nonincubated diabetic rats. NE-stimulated p110 PI3-K activity was elevated in aortas from diabetic rats coincubated with a noncontractile dose of ANG II. These results suggest that, in insulin-treated Type 1 diabetic rats with hyperinsulinemia, chronic ANG II type 1 receptor blockade blunts the increases in vascular contractility and blood pressure via a decrease in p110 delta-associated PI3-K activity.AJP Heart and Circulatory Physiology 09/2006; 291(2):H846-53. · 3.71 Impact Factor