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      Altered Expression of Na +/H + Exchanger Isoforms 1 and 3 in Clipped and Unclipped Kidneys of a 2-Kidney-1-Clip Goldblatt Model of Hypertension

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          Background: Functional differences between the clipped and unclipped kidneys in a 2-kidney-1-clip (2K-1C) hypertension model have been reported. However, the molecular basis of these changes is poorly understood. Objectives: Expression of NHE-1 and NHE-3 isoforms and sodium pump activity (PNP), and their modulation by blood pressure (BP), PGE<sub>2</sub> and TXB<sub>2</sub> were examined in the kidneys of 2K-1C rats treated with cilazapril for short- (4 and 24 h) and long-term (7 days) periods. Methods: 2K-1C rats were divided into two groups. Group 1 (short-term) animals were treated with a single dose of cilazapril for 4 or 24 h. Group 2 (long-term) animals received a daily dose of cilazapril for 7 days. 2K-1C animals receiving water served as clipped controls, and sham-operated animals were normal controls. Western blot analysis was used to estimate the protein levels and ELISA for PGE<sub>2</sub> and TXB<sub>2</sub>. Results: Levels of NHE-1 and NHE-3 protein in the unclipped kidneys of both treatment groups were increased, whereas levels of α-actin, PNP activity and crude microsomes remained unchanged. These changes were significantly reduced by long-term, and not by short-term treatment with cilazapril. In group 1 clipped kidneys, NHE-3 and α-actin proteins were increased, and crude microsomes and PNP activity were decreased. In group 2 clipped kidneys, both NHE-1 and 3 isoforms were induced, whereas PNP activity was decreased. Cilazapril did not reverse the changes in the clipped kidneys in both groups, but reduced the crude microsomes. Group 2 unclipped kidneys showed hypertrophy, which remained unaffected by cilazapril treatment. Induced levels of BP, PGE<sub>2</sub> and TXB<sub>2</sub> in both groups were reduced significantly except for the 24-hour post-cilazapril treatment. Conclusions: These findings demonstrate a differential expression of NHE-1 and NHE-3 isoforms which is dependent on the rise in BP, PGE<sub>2</sub> or TXB<sub>2</sub> in the long-term treatment group, but not in the short-term treatment group. Thus, the changes in NHE isoforms and sodium pump activity, together, contribute to functional differences that exist in the 2K-1C kidneys.

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          Most cited references 5

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          Identification of a mitochondrial Na+/H+ exchanger.

          The electroneutral exchange of protons for Na+ and K+ across the mitochondrial inner membrane contributes to organellar volume and Ca2+ homeostasis. The molecular nature of these transporters remains unknown. In this report, we characterize a novel gene (YDR456w; renamed NHA2) in Saccharomyces cerevisiae whose deduced protein sequence is homologous to members of the mammalian Na+/H+ exchanger gene family. Fluorescence microscopy showed that a Nha2-green fluorescent protein chimera colocalizes with 4',6-diamidino-2-phenylindole staining of mitochondrial DNA. To assess the function of Nha2, we deleted the NHA2 gene by homologous disruption and found that benzamil-inhibitable, acid-activated 22Na+ uptake into mitochondria was abolished in the mutant strain. It also showed retarded growth on nonfermentable carbon sources and severely reduced survival during the stationary phase of the cell cycle compared with the parental strain, consistent with a defect in aerobic metabolism. Sequence comparisons revealed that Nha2 has highest identity to a putative Na+/H+ exchanger homologue (KIAA0267; renamed NHE6) in humans. Northern blot analysis demonstrated that NHE6 is ubiquitously expressed but is most abundant in mitochondrion-rich tissues such as brain, skeletal muscle, and heart. Fluorescence microscopy showed that a NHE6-green fluorescent protein chimera also accumulates in mitochondria of transfected HeLa cells. These data indicate that NHA2 and NHE6 encode homologous Na+/H+ exchangers and suggest they may be important for mitochondrial function in lower and higher eukaryotes, respectively.
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            The Expanding Family of Eucaryotic Na+/H+Exchangers

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              Increased proximal tubule NHE-3 and H+-ATPase activities in spontaneously hypertensive rats.

              To investigate renal proximal tubular sodium-hydrogen exchanger 3 (NHE-3) and H+-ATPase activities in young (5-week-old) spontaneously hypertensive rats (SHR) and normotensive Donryu (DRY) rats, in the period during which high blood pressure is developing.

                Author and article information

                S. Karger AG
                October 2002
                02 September 2002
                : 92
                : 2
                : 346-355
                aDepartment of Biochemistry, Faculty of Medicine, and bDepartment of Biological Sciences, Faculty of Science, Kuwait University, Kuwait
                63308 Nephron 2002;92:346–355
                © 2002 S. Karger AG, Basel

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                Figures: 4, Tables: 4, References: 48, Pages: 10
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