Both enalapril and losartan attenuate sarcolemmal Na+-K+-ATPase remodeling in failing rat heart due to myocardial infarction

To investigate the mechanisms underlying the depressed sarcolemmal (SL) Na(+)-K(+)-ATPase activity in congestive heart failure (CHF), different isoforms and gene expression of Na(+)-K(+)-ATPase were examined in the failing left ventricle (LV) at 8 weeks after myocardial infarction (MI). In view of the increased activity of renin-angiotensin system (RAS) in CHF, these parameters were also studied after 5 weeks of treatment with enalapril (10 mg x kg-1 x day-1), an angiotensin-converting enzyme inhibitor, and losartan (20 mg.kg-1.day-1), an angiotensin II type 1 receptor antagonist, starting at 3 weeks after the coronary ligation in rats. The infarcted animals showed LV dysfunction and depressed SL Na(+)-K(+)-ATPase activity. Protein content and mRNA levels for Na(+)-K(+)-ATPase alpha2 isoform were decreased whereas those for Na(+)-K(+)-ATPase alpha3 isoform were increased in the failing LV. On the other hand, no significant changes were observed in protein content or mRNA levels for Na(+)-K(+)-ATPase alpha1 and beta1 isoforms. The treatment of infarcted animals with enalapril or losartan improved LV function and attenuated the depression in Na(+)-K(+)-ATPase alpha2 isoform as well as the increase in alpha3 isoform, at both the protein and mRNA levels; however, combination therapy with enalapril and losartan did not produce any additive effects. These results provide further evidence that CHF due to MI is associated with remodeling of SL membrane and suggest that the blockade of RAS plays an important role in preventing these alterations in the failing heart.     

Angiotensin II stimulates H?-ATPase activity in intercalated cells from isolated mouse connecting tubules and cortical collecting ducts

Intercalated cells in the collecting duct system express V-type H(+)-ATPases which participate in acid extrusion, bicarbonate secretion, and chloride absorption depending on the specific subtype. The activity of H(+)-ATPases is regulated by acid-base status and several hormones, including angiotensin II and aldosterone. Angiotensin II stimulates chloride absorption mediated by pendrin in type B intercalated cells and this process is energized by the activity of H(+)-ATPases. Moreover, angiotensin II stimulates bicarbonate secretion by the connecting tubule (CNT) and early cortical collecting duct (CCD). In the present study we examined the effect of angiotensin II (10 nM) on H(+)-ATPase activity and localization in isolated mouse connecting tubules and cortical collecting ducts. Angiotensin II stimulated Na(+)-independent intracellular pH recovery about 2-3 fold, and this was abolished by the specific H(+)-ATPase inhibitor concanamycin. The effect of angiotensin II was mediated through type 1 angiotensin II receptors (AT(1)-receptors) because it could be blocked by saralasin. Stimulation of H(+)-ATPase activity required an intact microtubular network--it was completely inhibited by colchicine. Immunocytochemistry of isolated CNT/CCDs incubated in vitro with angiotensin II suggests enhanced membrane associated staining of H(+)-ATPases in pendrin expressing intercalated cells. In summary, angiotensin II stimulates H(+)-ATPases in CNT/CCD intercalated cells, and may contribute to the regulation of chloride absorption and bicarbonate secretion in this nephron segment.     

Modification of sarcolemmal Na+-K+-ATPase and Na+/Ca2+ exchanger expression in heart failure by blockade of renin-angiotensin system

The activities of both sarcolemmal (SL) Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchanger, which maintain the intracellular cation homeostasis, have been shown to be depressed in heart failure due to myocardial infarction (MI). Because the renin-angiotensin system (RAS) is activated in heart failure, this study tested the hypothesis that attenuation of cardiac SL changes in congestive heart failure (CHF) by angiotensin-converting enzyme (ACE) inhibitors is associated with prevention of alterations in gene expression for SL Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchanger. CHF in rats due to MI was induced by occluding the coronary artery, and 3 wk later the animals were treated with an ACE inhibitor, imidapril (1 mg.kg(-1).day(-1)), for 4 wk. Heart dysfunction and cardiac hypertrophy in the infarcted animals were associated with depressed SL Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchange activities. Protein content and mRNA levels for Na(+)/Ca(2+) exchanger as well as Na(+)-K(+)-ATPase alpha(1)-, alpha(2)- and beta(1)-isoforms were depressed, whereas those for alpha(3)-isoform were increased in the failing heart. These changes in SL activities, protein content, and gene expression were attenuated by treating the infarcted animals with imidapril. The beneficial effects of imidapril treatment on heart function and cardiac hypertrophy as well as SL Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchange activities in the infarcted animals were simulated by enalapril, an ACE inhibitor, and losartan, an angiotensin receptor antagonist. These results suggest that blockade of RAS in CHF improves SL Na(+)-K(+)-ATPase and Na(+)/Ca(2+) exchange activities in the failing heart by preventing changes in gene expression for SL proteins.     

Angiotensin II modulates the activity of Na+,K+-ATPase in cultured rat astrocytes via the AT1 receptor and protein kinase C-delta activation

In astrocytes the activity of the Na+,K(+)-ATPase pump maintains an inwardly directed electrochemical sodium gradient used by the Na+-dependent transporters and regulates the extracellular K+ concentration essential for neuronal excitability. We show here that incubation of cultured rat astrocytes with angiotensin II (Ang II) modulates Na+,K(+)-ATPase activity, in a dose- and time-dependent manner. Na+,K(+)-ATPase activation was mediated by binding of Ang II to AT1 receptors as it was completely blocked by DuP 753, a specific AT1 receptor subtype antagonist. Stimulation of Na+,K(+)-ATPase activity by Ang II was dependent on protein kinase C (PKC) activation because PKC antagonists abolished the inducing effect of Ang II and the PKC activator phorbol 12-myristate 13-acetate enhanced transporter activity. Ang II stimulated translocation of PKC-delta but not that of other PKC isoforms from the cytosol to the plasma membrane. These results indicate that the activity of Na+,K(+)-ATPase in astrocytes is increased by physiological concentrations of Ang II and that the AT1 receptor subtype mediates the Na+,K(+)-ATPase response to Ang II via PKC-delta activation.     

Increased colonic sodium absorption in rats with chronic renal failure is partially mediated by AT1 receptor agonism

To test the hypothesis that colonic Na(+) transport is altered in the 5/6 nephrectomized rat model of chronic renal failure (CRF), we measured Na(+) fluxes across distal colon from control (CON), CRF, and CRF rats treated with the angiotensin II (ANG II) receptor antagonist losartan (+LOS). We also evaluated overall fluid and Na(+) balance and compared colonic protein and mRNA expression profiles for electroneutral [sodium-hydrogen exchanger (NHE)] and electrogenic Na(+) transport [epithelial sodium channel (ENaC)] in these groups. Consistent with a 60% enhancement in colonic Na(+) absorption in CRF, urinary Na(+) excretion increased by about 50% while serum Na(+) homeostasis was maintained. These CRF-induced changes in Na(+) handling were normalized by treatment with LOS. Net Na(+) absorption was also stimulated in in vitro tissues from CON rats following acute serosal addition of ANG II (10(-7) M), and this increase was blocked by AT(1) antagonism but not by an AT(2) antagonist. In CRF, colonic protein and mRNA expression variably increased for apical NHE2, NHE3, and ENaC alpha-, beta-, gamma-subunits, whereas expression of basolateral NHE1 and Na(+)-K(+)-ATPase (alpha-isoform) remained unaltered. Upregulation of the ENaC subunit mRNA was attenuated somewhat by LOS treatment. Previously, we showed that colonic AT(1) receptor protein is upregulated twofold in CRF, and here we find that AT(1) and AT(2) mRNA and AT(2) protein abundance is unchanged in CRF. We conclude that Na(+) absorption in CRF rat distal colon is increased due to elevated expression of proteins mediating electroneutral and electrogenic uptake and that it is partially mediated by AT(1) receptors.     

Na(+)-K(+)-ATPase is distributed to microvillous and basal membrane of the syncytiotrophoblast in human placenta

Despite its importance for placental function, syncytiotrophoblast Na(+)-K(+)-ATPase has not been studied in detail. We purified syncytiotrophoblast microvillous (MVM) and basal (BM) membranes from full-term human placenta. Western blotting with isoform-specific antibodies demonstrated the presence of the alpha(1)-subunit, but not the alpha(2)- or alpha(3)-subunits, in MVM and BM. Relative density per unit membrane protein in BM was 48 +/- 1% (mean +/- SE, n = 4, P < 0.02) of that in the MVM. The activity of Na(+)-K(+)-ATPase was lower in BM (1.4 +/- 0.14 micromol. mg(-1). min(-1), n = 8, P < 0.02) than in MVM (3.9 +/- 0.25 micromol. mg(-1). min(-1)). Immunocytochemistry confirmed the distribution of Na(+)-K(+)-ATPase to MVM and BM. These findings suggest that the syncytiotrophoblast represents a type of transporting epithelium different from the classical epithelia found in the small intestine and kidney, where Na(+)-K(+)-ATPase is confined to the basolateral membrane only. This unique polarization of the Na(+) pump does not, however, preclude a net transcellular transport of Na(+) to the fetus.     

Development of an AT<Subscript>2</Subscript>-deficient proximal tubule cell line for transport studies

Angiotensin II is a major regulatory peptide for proximal tubule Na(+) reabsorption acting through two distinct receptor subtypes: AT(1) and AT(2). Physiological or pathological roles of AT(2) have been difficult to unravel because angiotensin II can affect Na(+) transport either directly via AT(2) on luminal or peritubular plasma membranes of proximal tubule cells or indirectly via the renal vasculature. Furthermore, separate systemic and intratubular renin-angiotensin systems impart considerable complexity to angiotensin's regulation. A transport-competent, proximal tubule cell model that lacks AT(2) is a potentially useful tool to assess cellular angiotensin II regulation. To this end, AT(2)-receptor-deficient mice were bred with an Immortomouse, which harbors the thermolabile immortalization gene SV40 large-T antigen (Tag), and AT(2)-receptor-deficient [AT(2) (-/-)], Tag heterozygous [Tag (+/-)] F(2) offspring were selected for cell line generation. S1 proximal tubule segments were microdissected, and epithelial cell outgrowth was expanded in culture. Cells that formed confluent, electrically resistive monolayers were selected for cryopreservation, and one isolate was extensively characterized for conductance (2 mS/cm(2)), short-circuit current (Isc; 0.2 microA/cm(2)), and proximal tubule-specific Na3(+) - succinate (DeltaIsc = 0.8 microA/cm(2) at 2 mM succinate) and Na3(+) - phosphate cotransport (DeltaIsc = 3 microA/cm(2) at 1 mM phosphate). Light microscopy showed a uniform, cobblestone-shaped monolayer with prominent cilia and brush borders. AT(2) receptor functionality, as demonstrated by angiotensin II inhibition of ANF-stimulated cGMP synthesis, was absent in AT(2)-deficient cells but prominent in wild-type cells. This transport competent cell line in conjunction with corresponding wild type and AT(1)-deficient lines should help explain angiotensin II signaling relevant to Na(+) transport.     

Mechanical stretching of alveolar epithelial cells increases Na(+)-K(+)-ATPase activity.

Alveolar epithelial cells effect edema clearance by transporting Na(+) and liquid out of the air spaces. Active Na(+) transport by the basolaterally located Na(+)-K(+)-ATPase is an important contributor to lung edema clearance. Because alveoli undergo cyclic stretch in vivo, we investigated the role of cyclic stretch in the regulation of Na(+)-K(+)-ATPase activity in alveolar epithelial cells. Using the Flexercell Strain Unit, we exposed a cell line of murine lung epithelial cells (MLE-12) to cyclic stretch (30 cycles/min). After 15 min of stretch (10% mean strain), there was no change in Na(+)-K(+)-ATPase activity, as assessed by (86)Rb(+) uptake. By 30 min and after 60 min, Na(+)-K(+)-ATPase activity was significantly increased. When cells were treated with amiloride to block amiloride-sensitive Na(+) entry into cells or when cells were treated with gadolinium to block stretch-activated, nonselective cation channels, there was no stimulation of Na(+)-K(+)-ATPase activity by cyclic stretch. Conversely, cells exposed to Nystatin, which increases Na(+) entry into cells, demonstrated increased Na(+)-K(+)-ATPase activity. The changes in Na(+)-K(+)-ATPase activity were paralleled by increased Na(+)-K(+)-ATPase protein in the basolateral membrane of MLE-12 cells. Thus, in MLE-12 cells, short-term cyclic stretch stimulates Na(+)-K(+)-ATPase activity, most likely by increasing intracellular Na(+) and by recruitment of Na(+)-K(+)-ATPase subunits from intracellular pools to the basolateral membrane.     

Angiotensin IV in the central nervous system

The mammalian brain harbors a renin-angiotensin system (RAS), which is independent from the peripheral RAS. Angiotensin II is a well-studied member of the RAS and exerts most of the known angiotensin-mediated effects on fluid and electrolyte homeostasis, autonomic activity, neuroendocrine regulation, and behavior. This review summarizes a mass of compelling new evidence for the biological role of an active (3-8) fragment of angiotensin II, named angiotensin IV. Angiotensin IV binds to a widely distributed binding site in the brain, but which is different from the known angiotensin II receptors AT1 and AT2. Angiotensin IV has been implicated in a number of physiological actions, including the regulation of blood flow, the modulation of exploratory behavior, and processes attributed to learning and memory. Furthermore, angiotensin IV may also be involved in neuronal development. Collectively, the available evidence suggests that angiotensin IV is a potent neuropeptide, involved in a broad range of brain functions.     

Dexamethasone prevents transport inhibition by hypoxia in rat lung and alveolar epithelial cells by stimulating activity and expression of Na+-K+-ATPase and epithelial Na+ channels

Hypoxia inhibits Na and lung fluid reabsorption, which contributes to the formation of pulmonary edema. We tested whether dexamethasone prevents hypoxia-induced inhibition of reabsorption by stimulation of alveolar Na transport. Fluid reabsorption, transport activity, and expression of Na transporters were measured in hypoxia-exposed rats and in primary alveolar type II (ATII) cells. Rats were treated with dexamethasone (DEX; 2 mg/kg) on 3 consecutive days and exposed to 10% O(2) on the 2nd and 3rd day of treatment to measure hypoxia effects on reabsorption of fluid instilled into lungs. ATII cells were treated with DEX (1 muM) for 3 days before exposure to hypoxia (1.5% O(2)). In normoxic rats, DEX induced a twofold increase in alveolar fluid clearance. Hypoxia decreased reabsorption (-30%) by decreasing its amiloride-sensitive component; pretreatment with DEX prevented the hypoxia-induced inhibition. DEX increased short-circuit currents (ISC) of ATII monolayers in normoxia and blunted hypoxic transport inhibition by increasing the capacity of Na(+)-K(+)-ATPase and epithelial Na(+) channels (ENaC) and amiloride-sensitive ISC. DEX slightly increased the mRNA of alpha- and gamma-ENaC in whole rat lung. In ATII cells from DEX-treated rats, mRNA of alpha(1)-Na(+)-K(+)-ATPase and alpha-ENaC increased in normoxia and hypoxia, and gamma-ENaC was increased in normoxia only. DEX stimulated the mRNA expression of alpha(1)-Na(+)-K(+)-ATPase and alpha-, beta-, and gamma-ENaC of A549 cells in normoxia and hypoxia (1.5% O(2)) when DEX treatment was begun before or during hypoxic exposure. These results indicate that DEX prevents inhibition of alveolar reabsorption by hypoxia and stimulates the expression of Na transporters even when it is applied in hypoxia.     

Depressed Na+-K+-ATPase activity in skeletal muscle at fatigue is correlated with increased Na+-K+-ATPase mRNA expression following intense exercise

We investigated whether depressed muscle Na(+)-K(+)-ATPase activity with exercise reflected a loss of Na(+)-K(+)-ATPase units, the time course of its recovery postexercise, and whether this depressed activity was related to increased Na(+)-K(+)-ATPase isoform gene expression. Fifteen subjects performed fatiguing, knee extensor exercise at approximately 40% maximal work output per contraction. A vastus lateralis muscle biopsy was taken at rest, fatigue, 3 h, and 24 h postexercise and analyzed for maximal Na(+)-K(+)-ATPase activity via 3-O-methylfluorescein phosphatase (3-O-MFPase) activity, Na(+)-K(+)-ATPase content via [(3)H]ouabain binding sites, and Na(+)-K(+)-ATPase alpha(1)-, alpha(2)-, alpha(3)-, beta(1)-, beta(2)- and beta(3)-isoform mRNA expression by real-time RT-PCR. Exercise [352 (SD 267) s] did not affect [(3)H]ouabain binding sites but decreased 3-O-MFPase activity by 10.7 (SD 8)% (P < 0.05), which had recovered by 3 h postexercise, without further change at 24 h. Exercise elevated alpha(1)-isoform mRNA by 1.5-fold at fatigue (P < 0.05). This increase was inversely correlated with the percent change in 3-O-MFPase activity from rest to fatigue (%Delta3-O-MFPase(rest-fatigue)) (r = -0.60, P < 0.05). The average postexercise (fatigue, 3 h, 24 h) alpha(1)-isoform mRNA was increased 1.4-fold (P < 0.05) and approached a significant inverse correlation with %Delta3-O-MFPase(rest-fatigue) (r = -0.56, P = 0.08). Exercise elevated alpha(2)-isoform mRNA at fatigue 2.5-fold (P < 0.05), which was inversely correlated with %Delta3-O-MFPase(rest-fatigue) (r = -0.60, P = 0.05). The average postexercise alpha(2)-isoform mRNA was increased 2.2-fold (P < 0.05) and was inversely correlated with the %Delta3-O-MFPase(rest-fatigue) (r = -0.68, P < 0.05). Nonsignificant correlations were found between %Delta3-O-MFPase(rest-fatigue) and other isoforms. Thus acute exercise transiently decreased Na(+)-K(+)-ATPase activity, which was correlated with increased Na(+)-K(+)-ATPase gene expression. This suggests a possible signal-transduction role for depressed muscle Na(+)-K(+)-ATPase activity with exercise.     

Tissue ATPase activity and recovery in the freshwater crab Oziotelphusa senex senex exposed to a sublethal concentration of endosulfan for varying periods of time.

1. Na(+)-K+ and Mg(2+)-tissue ATPases of the freshwater crab Oziotelphusa senex senex showed increasing inhibition when exposed to a sublethal concentration (1.86 mg/l = 0.1 of LC50) of endosulfan for 1-30 days. 2. Na(+)-K(+)-ATPase activity in all tissues (thoracic nerve mass, gill, hepatopancreas and claw muscle) was higher than Mg(2+)-ATPase activity. 3. After 30 days exposure tissue Mg(2+)-ATPase was less affected than Na(+)-K(+)-ATPase. 4. Crabs exposed to endosulfan and then returned to uncontaminated water showed greater recovery of Mg(2+)-ATPase than Na(+)-K(+)-ATPase with 90-95% recovery after 1 day exposure and 60-65% recovery after 30 days exposure. 5. Changes in behaviour of the crabs were noted after 7 days exposure to endosulfan with progressive loss of coordination, decreased activity and increased exudation of mucus.     

Placental insufficiency results in temporal alterations in the renin angiotensin system in male hypertensive growth restricted offspring

Reduced uterine perfusion initiated in late gestation in the rat results in intrauterine growth restriction (IUGR) and development of hypertension by 4 wk of age. We hypothesize that the renin angiotensin system (RAS), a regulatory system important in the long-term control of blood pressure, may be programmed by placental insufficiency and may contribute to the etiology of IUGR hypertension. We previously reported that RAS blockade abolished hypertension in adult IUGR offspring; however, the mechanisms responsible for the early phase of hypertension are unresolved. Therefore, the purpose of this study was to examine RAS involvement in early programmed hypertension and to determine whether temporal changes in RAS expression are observed in IUGR offspring. Renal renin and angiotensinogen mRNA expression were significantly decreased at birth (80 and 60%, respectively); plasma and renal RAS did not differ in conjunction with hypertension (mean increase of 14 mmHg) in young IUGR offspring; however, hypertension (mean increase of 22 mmHg) in adult IUGR offspring was associated with marked increases in renal angiotensin-converting enzyme (ACE) activity (122%) and renal renin and angiotensinogen mRNA (7-fold and 7.4-fold, respectively), but no change in renal ANG II or angiotensin type 1 receptor. ACE inhibition (enalapril, 10 mg x kg(-1) x day(-1), administered from 2 to 4 wk of age) abolished hypertension in IUGR at 4 wk of age (decrease of 15 mmHg, respectively) with no significant depressor effect in control offspring. Therefore, temporal alterations in renal RAS are observed in IUGR offspring and may play a key role in the etiology of IUGR hypertension.     

Regulation of fish gill Na(+)-K(+)-ATPase by selective sulfatide-enriched raft partitioning during seawater adaptation

Na(+)-K(+)-ATPase is arguably the most important enzyme in the animal cell plasma membrane, but the role of the membrane in its regulation is poorly understood. We investigated the relationship between Na(+)-K(+)-ATPase and membrane microdomains or "lipid rafts" enriched in sulfatide (sulfogalactosylceramide/SGC), a glycosphingolipid implicated as a cofactor for this enzyme, in the basolateral membrane of rainbow trout gill epithelium. Our studies demonstrated that when trout adapt to seawater (33 ppt), Na(+)-K(+)-ATPase relocates to these structures. Arylsulfatase-induced desulfation of basolateral membrane SGC prevented this relocation and significantly reduced Na(+)-K(+)-ATPase activity in seawater but not freshwater trout. We contend that Na(+)-K(+)-ATPase partitions into SGC-enriched rafts to help facilitate the up-regulation of its activity during seawater adaptation. We also suggest that differential partitioning of Na(+)-K(+)-ATPase between these novel SGC-enriched regulatory platforms results in two distinct, physiological Na(+) transport modes. In addition, we extend the working definition of cholesterol-dependent raft integrity to structural dependence on the sulfate moiety of SGC in this membrane.     

Upregulation of apical NHE3 in renal OK cells overexpressing the rodent alpha(1)-subunit of the Na(+) pump

Vectorial Na(+) reabsorption across the proximal tubule is mediated by apical entry of Na(+), primarily via Na(+)/H(+) exchanger isoform 3 (NHE3), and basolateral extrusion via the Na(+) pump (Na(+)-K(+)-ATPase). We hypothesized that regulation of Na(+) reabsorption should involve not only the activity of the basolateral Na(+)-K(+)-ATPase, but also the apical NHE3, in a concerted manner. To generate a cell line that overexpresses Na(+)-K(+)-ATPase, opossum kidney (OK) cells were transfected with the rodent Na(+)-K(+)-ATPase alpha(1)-subunit (pCMV ouabain vector), and native cells were used as a control. The existence of distinct functional classes of Na(+)-K(+)-ATPase in wild-type and transfected cells was confirmed by the inhibition profile of Na(+)-K(+)-ATPase activity by ouabain. In contrast to wild-type cells, transfected cells exhibited two IC(50) values for ouabain: the first value was similar to the IC(50) of control cells, and the second value was 2 log units greater than the first, consistent with the presence of rat and opossum alpha(1)-isozymes. It is shown that transfection of OK cells with Na(+)-K(+)-ATPase increased Na(+)-K(+)-ATPase and NHE3 activities. This was associated with overexpression of the Na(+)-K(+)-ATPase alpha(1)-subunit and NHE3 in transfected OK cells. The abundance of the Na(+)-K(+)-ATPase beta(1)-subunit was slightly lower in transfected OK cells. In conclusion, the increase in expression and function of Na(+)-K(+)-ATPase in cells transfected with the rodent Na(+) pump alpha(1)-subunit cDNA is expected to stimulate apical Na(+) influx into the cells, thereby accounting for the observed stimulation of the apical NHE3 activity.     

Role of brain renin angiotensin system in neurodegeneration: An update

Renin angiotensin system (RAS) is an endocrine system widely known for its physiological roles in electrolyte homeostasis, body fluid volume regulation and cardiovascular control in peripheral circulation. However, brain RAS is an independent form of RAS expressed locally in the brain, which is known to be involved in brain functions and disorders. There is strong evidence for a major involvement of excessive brain angiotensin converting enzyme (ACE)/Angiotensin II (Ang II)/Angiotensin type-1 receptor (AT-1R) axis in increased activation of oxidative stress, apoptosis and neuroinflammation causing neurodegeneration in several brain disorders. Numerous studies have demonstrated strong neuroprotective effects by blocking AT1R in these brain disorders. Additionally, the angiotensin converting enzyme 2 (ACE2)/Angiotensin (1–7)/Mas receptor (MASR), is another axis of brain RAS which counteracts the damaging effects of ACE/Ang II/AT1R axis on neurons in the brain. Thus, angiotensin II receptor blockers (ARBs) and activation of ACE2/Angiotensin (1–7)/MASR axis may serve as an exciting and novel method for neuroprotection in several neurodegenerative diseases. Here in this review article, we discuss the expression of RAS in the brain and highlight how altered RAS level may cause neurodegeneration. Understanding the pathophysiology of RAS and their links to neurodegeneration has enormous potential to identify potentially effective pharmacological tools to treat neurodegenerative diseases in the brain.     

Dopamine regulation of Na+-K+-ATPase requires the PDZ-2 domain of sodium hydrogen regulatory factor-1 (NHERF-1) in opossum kidney cells

Na(+)-K(+)-ATPase activity in renal proximal tubule is regulated by several hormones including parathyroid hormone (PTH) and dopamine. The current experiments explore the role of Na(+)/H(+) exchanger regulatory factor 1 (NHERF-1) in dopamine-mediated regulation of Na(+)-K(+)-ATPase. We measured dopamine regulation of ouabain-sensitive (86)Rb uptake and Na(+)-K(+)-ATPase α1 subunit phosphorylation in wild-type opossum kidney (OK) (OK-WT) cells, OKH cells (NHERF-1-deficient), and OKH cells stably transfected with full-length human NHERF-1 (NF) or NHERF-1 constructs with mutated PDZ-1 (Z1) or PDZ-2 (Z2) domains. Treatment with 1 μM dopamine decreased ouabain-sensitive (86)Rb uptake, increased phosphorylation of Na(+)-K(+)-ATPase α1-subunit, and enhanced association of NHERF-1 with D1 receptor in OK-WT cells but not in OKH cells. Transfection with wild-type, full-length, or PDZ-1 domain-mutated NHERF-1 into OKH cells restored dopamine-mediated regulation of Na(+)-K(+)-ATPase and D1-like receptor association with NHERF-1. Dopamine did not regulate Na(+)-K(+)-ATPase or increase D1-like receptor association with NHERF-1 in OKH cells transfected with mutated PDZ-2 domain. Dopamine stimulated association of PKC-ζ with NHERF-1 in OK-WT and OKH cells transfected with full-length or PDZ-1 domain-mutated NHERF-1 but not in PDZ-2 domain-mutated NHERF-1-transfected OKH cells. These results suggest that NHERF-1 mediates Na(+)-K(+)-ATPase regulation by dopamine through its PDZ-2 domain.     

Angiotensin II stimulates renal proximal tubule Na(+)-ATPase activity through the activation of protein kinase C

Recently, our group described an AT(1)-mediated direct stimulatory effect of angiotensin II (Ang II) on the Na(+)-ATPase activity of proximal tubules basolateral membranes (BLM) [Am. J. Physiol. 248 (1985) F621]. Data in the present report suggest the participation of a protein kinase C (PKC) in the molecular mechanism of Ang II-mediated stimulation of the Na(+)-ATPase activity due to the following observations: (i) the stimulation of protein phosphorylation in BLM, induced by Ang II, is mimicked by the PKC activator TPA, and is completely reversed by the specific PKC inhibitor, calphostin C; (ii) the Na(+)-ATPase activity is stimulated by Ang II and TPA in the same magnitude, being these effects abolished by the use of the PKC inhibitors, calphostin C and sphingosine; (iii) the Na(+)-ATPase activity is activated by catalytic subunit of PKC (PKC-M), in a similar and nonadditive manner to Ang II; and (iv) Ang II stimulates the phosphorylation of MARCKS, a specific substrate for PKC.