Characterization and localization of ouabain-insensitive Na-dependent ATPase activities along the rat nephron

Cellular Pathophysiology of Leptospirosis: Role of Na/K-ATPase

Inada and Ido identified Leptospira sp. as the pathogen responsible for Weil's Disease in 1915. Later, it was confirmed that Leptospira causes leptospirosis. The host microorganism's interaction at the cellular level remained misunderstood for many years. Although different bacterial components have been isolated and purified, the complexity of the molecular interactions between these components and the host and the molecular mechanisms responsible for the systemic dysfunctions still needs to be fully unveiled. Leptospirosis affects virtually all animal species. Its cellular pathophysiology must involve a ubiquitous cellular mechanism in all eukaryotes. Na/K-ATPase is the molecular target of the leptospiral endotoxin (glycolipoprotein-GLP). Na/K-ATPase dysfunctions on different types of cells give rise to the organ disorders manifested in leptospirosis. Concomitantly, the development of a peculiar metabolic disorder characterized by dyslipidemia, with increased levels of circulating free fatty acids and an imbalance in the fatty acid/albumin molar ratio, triggers events of cellular lipotoxicity. Synergistically, multiple molecular stimuli are prompted during the infection, activating inflammasomes and Na/K-ATPase signalosome, leading to pro-inflammatory and metabolic alterations during leptospirosis. Leptospirosis involves diverse molecular mechanisms and alteration in patient inflammatory and metabolic status. Nonetheless, Na/K-ATPase is critical in the disease, and it is targeted by GLP, its components, and other molecules, such as fatty acids, that inhibit or trigger intracellular signaling through this enzyme. Herein, we overview the role of Na/K-ATPase during leptospirosis infection as a potential therapeutic target or an indicator of disease severity.

Reducing ischemic kidney injury through application of a synchronization modulation electric field to maintain Na+/K+-ATPase functions

Renal ischemia-reperfusion injury is an important contributor to the development of delayed graft function after transplantation, which is associated with higher rejection rates and poorer long-term outcomes. One of the earliest impairments during ischemia is Na⁺/K⁺-ATPase (Na/K pump) dysfunction due to insufficient ATP supply, resulting in subsequent cellular damage. Therefore, strategies that preserve ATP or maintain Na/K pump function may limit the extent of renal injury during ischemia-reperfusion. Here, we applied a synchronization modulation electric field to activate Na/K pumps, thereby maintaining cellular functions under ATP-insufficient conditions. We tested the effectiveness of this technique in two models of ischemic renal injury: an in situ renal ischemia-reperfusion injury model (predominantly warm ischemia) and a kidney transplantation model (predominantly cold ischemia). Application of the synchronization modulation electric field to a renal ischemia-reperfusion injury mouse model preserved Na/K pump activity, thereby reducing kidney injury, as reflected by 40% lower plasma creatinine (1.17 ± 0.03 mg/dl) in the electric field-treated group as compared to the untreated control group (1.89 ± 0.06 mg/dl). In a mouse kidney transplantation model, renal graft function was improved by more than 50% with the application of the synchronization modulation electric field according to glomerular filtration rate measurements (85.40 ± 12.18 μl/min in the untreated group versus 142.80 ± 11.65 μl/min in the electric field-treated group). This technique for preserving Na/K pump function may have therapeutic potential not only for ischemic kidney injury but also for other diseases associated with Na/K pump dysfunction due to inadequate ATP supply.

Simple capacitor-switch model of excitatory and inhibitory neuron with all parts biologically explained allows input fire pattern dependent chaotic oscillations

Due to known information processing capabilities of the brain, neurons are modeled at many different levels. Circuit theory is also often used to describe the function of neurons, especially in complex multi-compartment models, but when used for simple models, there is no subsequent biological justification of used parts. We propose a new single-compartment model of excitatory and inhibitory neuron, the capacitor-switch model of excitatory and inhibitory neuron, as an extension of the existing integrate-and-fire model, preserving the signal properties of more complex multi-compartment models. The correspondence to existing structures in the neuronal cell is then discussed for each part of the model. We demonstrate that a few such inter-connected model units are capable of acting as a chaotic oscillator dependent on fire patterns of the input signal providing a complex deterministic and specific response through the output signal. The well-known necessary conditions for constructing a chaotic oscillator are met for our presented model. The capacitor-switch model provides a biologically-plausible concept of chaotic oscillator based on neuronal cells.

Inhibition of renal Na+-ATPase activity by inosine is mediated by A1 receptor-induced inhibition of the cAMP signaling pathway

We have previously demonstrated that adenosine is deaminated to inosine in the isolated basolateral membrane (BLM) of kidney proximal tubules. This work investigates the possible effect of inosine on proximal tubule Na(+)-ATPase activity. Inosine reduced Na(+)-ATPase activity by 70%. This effect of inosine was completely attenuated by 10(-8) M DPCPX, an A(1) receptor-selective antagonist, but it was not affected by either 10(-8) M DMPX or 10(-7) M MRS1523, A(2) and A(3) receptor-selective antagonists, respectively. The inhibitory effect of inosine was blocked by: (1) 10(-6) M GDPbetaS, a trimeric G protein inhibitor; (2) 1microg/ml pertussis toxin, a Gi protein inhibitor; (3) 10(-6) M forskolin, an adenylyl cyclase activator; (4) 10(-9) M cholera toxin, a Gs protein activator; (5) 10(-6)M cAMP. Our results demonstrate that the inhibitory effect of inosine on the sodium pump is mediated by the A(1) receptor/Gi/cAMP pathway.

Crosstalk between the signaling pathways triggered by angiotensin II and adenosine in the renal proximal tubules: implications for modulation of Na(+)-ATPase activity

We have previously demonstrated that adenosine (Ado) reverses the stimulatory effect of angiotensin II (Ang II) on Na(+)-ATPase activity via the A(2A) receptor. In this work, the molecular mechanism involved in Ado-induced shutdown in the signaling pathway triggered by 10(-8)M Ang II was investigated. It was observed that: (1) both 10(-12)M PMA (a PKC activator) and 5x10(-8)M U73122 (an inhibitor of PI-PLCbeta) prevent the reversion effect induced by 10(-6)M Ado (only observed in the presence of 10(-6)M DPCPX (an A(1) receptor antagonist)) on Ang II-stimulated Na(+)-ATPase and PKC activities; (2) Ang II-stimulated PKC activity was reversed by 10(-6)M forskolin (an adenylyl cyclase activator) or 10(-8)M PKA inhibitory peptide and 10(-8)M DMPX (an A(2) receptor-selective antagonist). Considering that PMA prevents the inhibitory effect of Ado on Ang II-stimulated Na(+)-ATPase and PKC activities, it is likely that the PMA-induced effect, i.e. PKC activation, is downstream of the target for Ado-induced reversion of Ang II stimulation of Na(+)-ATPase activity. We investigated the hypothesis that PI-PLCbeta could be the target for Ado-induced PKA activation. Our data demonstrate that Ang II-stimulated PI-PLCbeta activity was reversed by Ado or 10(-7)M cAMP; the reversibility of the Ado-induced effect was prevented by either DMPX or PKA inhibitory peptide. These data demonstrate that Ado-induced PKA activation reduces Ang II-induced stimulation of PI-PLCbeta.

B2 receptor-mediated dual effect of bradykinin on proximal tubule Na+ -ATPase: sequential activation of the phosphoinositide-specific phospholipase Cbeta/protein kinase C and Ca2+ -independent phospholipase A2 pathways

In a previous paper we showed that bradykinin (BK), interacting with its B2 receptor, inhibits proximal tubule Na+ -ATPase activity but does not change (Na+ +K+)ATPase activity. The aim of this paper was to investigate the molecular mechanisms involved in B2-mediated modulation of proximal tubule Na+ -ATPase by BK. To abolish B1 receptor-mediated effects, all experiments were carried out in the presence of (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Leu), des-Arg9-[Leu8]-BK (DALBK), a specific antagonist of B1 receptor. A dual effect on the Na+ -ATPase activity through the B2 receptor was found: short incubation times (1-10 min) stimulate the enzyme activity; long incubation times (10-60 min) inhibit it. The stimulatory effect of BK is mediated by activation of phosphoinositide-specific phospholipase C beta (PI-PLCbeta)/protein kinase C (PKC); its inhibitory action is mediated by Ca2+ -independent phospholipase A2 (iPLA2). Prior activation of the PI-PLCbeta/PKC pathway is required to activate the iPLA2-mediated inhibitory phase. These results reveal a new mechanism by which BK can modulate renal sodium excretion: coupling between B2 receptor and activation of membrane-associated iPLA2.

Adenosine reverses the stimulatory effect of angiotensin II on the renal Na+-ATPase activity through the A2 receptor

In the present paper, we report the modulation of the Angiotensin II (Ang II)-stimulated Na+-ATPase activity of the proximal tubule basolateral membrane by adenosine (Ado). Preincubation of isolated basolateral membrane with 10(-8)M Ang II increases the Na+-ATPase activity from 7.5+/-0.3 (control) to 14.6+/-0.9 nmol Pi x mg(-1)x min(-1)nmol Pi x mg(-1) x min(-1) (p<0.05). Incubation of Ang II-stimulated enzyme with 10(-6)M Ado, in the presence of the A1 receptor antagonist DPCPX (10(-6)M), completely reverses the Ang II-induced effect bringing the Na+-ATPase activity to the basal level. The following evidences demonstrate involvement of the A2 receptor/Gs protein/adenylyl cyclase/PKA signaling pathway in the inhibitory effect induced by Ado on the Ang II-stimulated Na+-ATPase activity in the presence of the DPCPX: 1) the inhibitory effect of Ado is abolished by the A2 receptor selective antagonist DMPX (10(-8)M); 2) the effect induced by Ado is blocked by 10(-8)M GDPbetaS and mimicked by 10(-9)M cholera toxin and 10(-8)M GTPgammaS; 3) the stimulatory effect of Ang II is reduced by 10(-6)M forskolin, an activator of adenylyl cyclase, or 10(-6)M cAMP; 4) Ado stimulates PKA activity; 5) the inhibitory effect induced by this nucleoside is reversed by the PKA inhibitor peptide.

Stimulation of the proximal tubule Na+-ATPase activity by adenosine A(2A) receptor

The aim of this work was to determine the molecular mechanism involved in the stimulation of the pig kidney proximal tubule Na+-ATPase by adenosine (Ado). To study the role of A2 Ado receptors, we added in all experiments 10(-6)M DPCPX, an A1 receptor-selective antagonist, since we have previously shown that Ado inhibits the enzyme activity through this receptor. Ado increased the Na+-ATPase activity with maximal effect observed at 10(-6)M. The presence of both A(2A) and A(2B) receptors were demonstrated by immunoblotting using specific polyclonal antibodies. The stimulatory effect of Ado was completely abolished by 5 x 10(-9)M DMPX, an antagonist of A2 receptor, and 10(-7)M SCH 58261, an A(2A) receptor-selective antagonist. DMPA (10(-7)M), a specific agonist of A(2A) receptor mimicked the stimulatory effect of Ado. Involvement of a Gs protein/adenylate cyclase/PKA pathway was evidenced by: (a) the reversion of Ado-induced effect by GDPbetaS; (b) stimulation of the Na+-ATPase activity in a similar and non-additive manner to Ado by 10(-8)M cholera toxin, 10(-7)M GTPgammaS, 10(-6)M forskolin, 10(-7)M cAMP or 1.25 U catalytic subunit of PKA; (c) the reversion of the stimulatory effect of Ado by 10(-8)M PKA inhibitor peptide; (d) Ado-produced two-fold increase of the PKA activity, which was completely reversed by 10(-6)M DMPX. These are the first evidences showing the modulation of a renal primary active sodium transporter by Ado through A(2A) receptor.

PLA2/PGE2 are involved in the inhibitory effect of bradykinin on the angiotensin-(1-7)-stimulated Na(+)-ATPase activity of the proximal tubule

Recently, we demonstrated that bradykinin (BK) counteracts the stimulatory effect of Ang-(1-7) on the Na(+)-ATPase activity from basolateral membrane of the proximal tubule through B2 receptor. In the present paper, the signaling pathway involved in the inhibitory response of the Na(+)-ATPase activity to BK was investigated. The following results indicate that the phospholipase A2 (PLA2)/COX/prostaglandin E (PGE2) pathway is implicated in this process: (1) The inhibitory effect of BK on Ang-(1-7)-stimulated enzyme is abolished in a dose-dependent manner by quinacrine (10(-9)-10(-6)M), a nonspecific PLA2 inhibitor, and by PACOCF3 (10(-7)M), an inhibitor of a Ca(2+)-independent PLA2. However, AACOCF3 (2 x 10(-4) M), an inhibitor of the cytosolic PLA2, does not modify the inhibitory effect of BK. (2) The inhibitory effect of BK on the Ang-(1-7)-stimulated enzyme is reversed by cyclooxygenase (COX) inhibitors diclofenac (10(-12) M) and indomethacin (10(-12) M). (3) PGE2 (10(-12)-10(-5) M) inhibits the Na(+)-ATPase activity in a dose dependent manner. (4)The inhibitory effects of PGE2 and BK on the Na(+)-ATPase activity are not cumulative. (5) PGE2 (10(-12)-10(-8) M) counteracts the stimulatory effect of Ang-(1-7) on the enzyme activity in a dose-dependent manner.

Bradykinin counteracts the stimulatory effect of angiotensin-(1-7) on the proximal tubule Na+ -ATPase activity through B2 receptor

Recently, we demonstrated that angiotensin-(1-7) (Ang-(1-7)) stimulates the Na(+)-ATPase activity through a losartan-sensitive angiotensin receptor, whereas bradykinin inhibits the enzyme activity through the B(2) receptor [Regul. Pept. 91 (2000) 45; Pharmacol. Rev. 32 (1980) 1]. In the present paper, the effect of bradykinin (BK) on Ang-(1-7)-stimulated Na(+)-ATPase activity was evaluated. Preincubation of Na(+)-ATPase with 10(-9) M Ang-(1-7) increases enzyme activity from 7.9+/-0.9 to 14.1+/-1.5 nmol Pi mg(-1) min(-1), corresponding to an increase of 79% (p<0.05). This effect is reverted by bradykinin in a dose-dependent manner (10(-14)-10(-8) M), reaching maximal inhibitory effect at 10(-9) M. Des-Arg(9) bradykinin (DABK), an agonist of B(1) receptor, at the concentrations of 10(-9)-10(-7) M, does not mimic the BK inhibitory effect, and des-Arg(9)-[Leu(8)]-BK (DALBK), a B(1) receptor antagonist, at the concentrations of 10(-10)-10(-7) M, does not prevent the inhibitory effect of BK on Ang-(1-7)-stimulated enzyme. On the other hand, HOE 140, an antagonist of B(2) receptor, abolishes the inhibitory effect of BK on the Ang-(1-7)-stimulated enzyme in a dose-dependent manner, reaching maximal effect at 10(-7) M. Taken together, these data indicate that stimulation of B(2) receptors by BK can counteract the stimulatory effect of Ang-(1-7) on the proximal tubule Na(+)-ATPase activity.

Differences in regulation of pH(i) in large (>/=10 nuclei) and small (</=5 nuclei) osteoclasts

Osteoclasts are multinucleated cells that resorb bone by extrusion of protons and proteolytic enzymes. They display marked heterogeneity in cell size, shape, and resorptive activity. Because high resorptive activity in vivo is associated with an increase in the average size of osteoclasts in areas of greater resorption and because of the importance of proton extrusion in resorption, we investigated whether the activity of the bafilomycin A(1)-sensitive vacuolar-type H(+)-ATPase (V-ATPase) and amiloride-sensitive Na(+)/H(+) exchanger differed between large and small osteoclasts. Osteoclasts were obtained from newborn rabbit bones, cultured on glass coverslips, and loaded with the pH-sensitive indicator 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Intracellular pH (pH(i)) was recorded in single osteoclasts by monitoring fluorescence. Large (>/=10 nuclei) and small (</=5 nuclei) osteoclasts differed in that large osteoclasts had a higher basal pH(i), their pH(i) was decreased by bafilomycin A(1) addition or removal of extracellular Na(+), and the realkalinization upon readdition of Na(+) was bafilomycin A(1) sensitive. After acid loading, a subpopulation of large osteoclasts (40%) recovered by V-ATPase activity alone, whereas all small osteoclasts recovered by Na(+)/H(+) exchanger activity. Interestingly, in 60% of the large osteoclasts, pH(i) recovery was mediated by both the Na(+)/H(+) exchanger and V-ATPase activity. Our results show a striking difference between pH(i) regulatory mechanisms of large and small osteoclasts that we hypothesize may be associated with differences in the potential resorptive activity of these cells.

Bradykinin modulates the ouabain-insensitive Na+-ATPase activity from basolateral membrane of the proximal tubule

This paper studies the modulation by bradykinin of the ouabain-insensitive Na+-ATPase activity in both renal cortex homogenate and basolateral membrane from proximal tubule. The increase in bradykinin concentration from 10-14 to 10-10 M stimulated the ouabain-insensitive Na+-ATPase activity in cortex homogenates about 2.2-fold, but inhibited the enzyme activity of basolateral membrane preparations by 60%. In both preparations, the maximal effect was obtained with 10-10 M bradykinin. Further increase in the concentration of bradykinin completely abolished these effects. The antagonist of the B2 receptor, Hyp3, completely abolished the effect of 10-10 M bradykinin on the Na+-ATPase activity in the basolateral membrane preparation in a dose-dependent manner, but had no effect on the bradykinin stimulated enzyme activity of the cortex homogenate. Furthermore, in the presence of 10-7 M Hyp3, 10-10 M bradykinin stimulated the Na+-ATPase activity by 45% in the basolateral membrane preparations. The increase in des-Arg9-bradykinin concentration from 10-12 to 10-7 M, an agonist of the B1 receptor, stimulated the Na+-ATPase activity of the cortex homogenates and of the basolateral membrane preparations by 105 and 148%, respectively. In the presence of 25 microM mergetpa, an inhibitor of kininase I, the increase in bradykinin concentration from 10-12 to 10-10 M promoted similar inhibition of the Na+-ATPase activity of both cortex homogenates and basolateral membrane preparations. These results suggest that bradykinin stimulated the Na+-ATPase activity of proximal tubule through the interaction with B1 receptors and inhibited the enzyme through the interaction with B2 receptors. Furthermore, the cortex homogenate expresses a kininase I activity that cleaves bradykinin to des-Arg9-bradykinin.

Ouabain-insensitive Na(+)-ATPase activity of Malpighian tubules from Rhodnius prolixus

In the present paper, we show the existence of a furosemide-sensitive Na(+)-stimulated, Mg(2+)-dependent ATPase activity in cell lysates of Malpighian tubular cells from Rhodnius prolixus, which could be the biochemical expression of the Na(+)-pump. The main characteristics of this activity are: (1) K0.5 for Na+ = 1.49 +/- 0.18 mM, (2) Vmax = 2.8 +/- 0.1 nmol inorganic orthophosphate (Pi).mg prot-1.min-1, (3) it is fully abolished by 2 mM furosemide, (4)it is insensitive to ouabain concentrations up to 10(-2) M, (5) it is sensitive to the presence of vanadate in the incubation medium indicating it to be a P-type ATPase, and (6) it is stimulated by nanomolar concentrations of Ca2+ in the incubation medium.

Effect of adenosine on the ouabain-insensitive Na+-ATPase activity from basolateral membrane of the proximal tubule

The regulation of the furosemide-sensitive Na+-ATPase activity and ouabain-sensitive (Na+ + K+)ATPase activities from proximal tubules by adenosine was investigated. When the concentration of adenosine was increased the furosemide-sensitive ATPase activity decreased with maximal inhibition at 10(-8) M (56% of inhibition). However, the (Na+ + K+)ATPase activity was not affected by adenosine. Theophylline, an antagonist of P1 adenosine receptor, completely reversed the effect of adenosine on the furosemide-sensitive ATPase activity in a dose-response manner. The adenosine effect was mimicked by N6-cyclohexyladenosine (CHA), an agonist for A1 adenosine receptor. 5'-N-ethylcarboxamideadenosine (NECA), an agonist for A2 adenosine receptor, did not affect the furosemide-sensitive ATPase activity. When adenosine was used in the presence of 1 microg ml(-1) pertussis toxin, a Gi protein inhibitor, no change in the furosemide-sensitive ATPase activity was observed. The addition of 1 nM cholera toxin increased the Na+-ATPase activity by 60%. Adenosine decreased the cholera toxin stimulated Na+-ATPase in 42%, similar to the effect observed in the absence of cholera toxin. Dibutyryl-cAMP reversed the effect of adenosine in a dose dependent manner while the protein kinase A peptide inhibitor mimicked it. These data are compatible with a modulatory effect of adenosine on the Na+-ATPase activity via A1 subtype receptor.

Triflocin, a novel inhibitor for the Na-HCO3 symport in the proximal tubule

1. Triflocin, applied at millimolar concentration hyperpolarizes the basolateral membrane of Necturus proximal convoluted tubular cells, in vivo. 2. Barium, 2.5 x 10(-3) M, ouabain, 10(-3) M, or amiloride 10(-4) M, fail to prevent this hyperpolarization. 3. Triflocin has no effect on the intracellular chloride activity. 4. In physiological acid base conditions, Triflocin increases intracellular pH. 5. Upon an acute isohydric hypercapnia, Triflocin depolarizes the basolateral membrane potential. 6. It is concluded that, Triflocin inhibits the basolateral electrogenic Na-(HCO3)n > 1 cotransport in proximal tubules.