MAPKinase and regulation of the sodium-proton exchanger in human red blood cell

Lysophosphatidic Acid-Activated Calcium Signaling Is Elevated in Red Cells from Sickle Cell Disease Patients

(1) Background: It is known that sickle cells contain a higher amount of Ca2+ compared to healthy red blood cells (RBCs). The increased Ca2+ is associated with the most severe symptom of sickle cell disease (SCD), the vaso-occlusive crisis (VOC). The Ca2+ entry pathway received the name of Psickle but its molecular identity remains only partly resolved. We aimed to map the involved Ca2+ signaling to provide putative pharmacological targets for treatment. (2) Methods: The main technique applied was Ca2+ imaging of RBCs from healthy donors, SCD patients and a number of transgenic mouse models in comparison to wild-type mice. Life-cell Ca2+ imaging was applied to monitor responses to pharmacological targeting of the elements of signaling cascades. Infection as a trigger of VOC was imitated by stimulation of RBCs with lysophosphatidic acid (LPA). These measurements were complemented with biochemical assays. (3) Results: Ca2+ entry into SCD RBCs in response to LPA stimulation exceeded that of healthy donors. LPA receptor 4 levels were increased in SCD RBCs. Their activation was followed by the activation of Gi protein, which in turn triggered opening of TRPC6 and CaV2.1 channels via a protein kinase Cα and a MAP kinase pathway, respectively. (4) Conclusions: We found a new Ca2+ signaling cascade that is increased in SCD patients and identified new pharmacological targets that might be promising in addressing the most severe symptom of SCD, the VOC.

Burn-Induced Apoptosis of Pulmonary Microvascular Endothelial Cell is NHE1 Dependent and Regulated by PI3K-Akt and p38 MAPK Pathways

Na/H exchanger 1 (NHE1) is a ubiquitously expressed protein on mammalian plasma membranes and involved in cell apoptosis and tissue injury. Our previous study found that NHE1 inhibition prevents burn-induced acute lung injury (ALI). However, the potential mechanism of NHE1 in burn-induced ALI is still unclear. This study investigated the role of NHE1 in burn-induced apoptosis of human pulmonary microvascular endothelial cells. Based on the western blot analyses, real-time PCR, fluorescence spectroscopy, and apoptosis analysis, we found that burn serum significantly induced NHE1 activation, promoted intracellular Na accumulation, and elevated apoptosis ratio. Inhibition of NHE1 with cariporide reversed burn-induced intracellular Na accumulation and cell apoptosis. Different doses of cariporide also significantly decreased Cai concentrations and calpain activity induced by burn serum. Furthermore, inhibition of PI3K contributed to the increase of NHE1 activation and cell apoptosis, whereas the inhibition of p38 MAPK led to inhibition of NHE1 activation and significant decreases of cell apoptosis. The data demonstrate that NHE1 activation facilitates burn-induced endothelial cell apoptosis, mediated by Ca-dependent pathway. PI3K-Akt and p38 MAPK were found to be upstream regulators of NHE1. This study provides new mechanisms underlying burn-induced ALI.

Diverse Stakeholders of Tumor Metabolism: An Appraisal of the Emerging Approach of Multifaceted Metabolic Targeting by 3-Bromopyruvate

Malignant cells possess a unique metabolic machinery to endure unobstructed cell survival. It comprises several levels of metabolic networking consisting of 1) upregulated expression of membrane-associated transporter proteins, facilitating unhindered uptake of substrates; 2) upregulated metabolic pathways for efficient substrate utilization; 3) pH and redox homeostasis, conducive for driving metabolism; 4) tumor metabolism-dependent reconstitution of tumor growth promoting the external environment; 5) upregulated expression of receptors and signaling mediators; and 6) distinctive genetic and regulatory makeup to generate and sustain rearranged metabolism. This feat is achieved by a "battery of molecular patrons," which acts in a highly cohesive and mutually coordinated manner to bestow immortality to neoplastic cells. Consequently, it is necessary to develop a multitargeted therapeutic approach to achieve a formidable inhibition of the diverse arrays of tumor metabolism. Among the emerging agents capable of such multifaceted targeting of tumor metabolism, an alkylating agent designated as 3-bromopyruvate (3-BP) has gained immense research focus because of its broad spectrum and specific antineoplastic action. Inhibitory effects of 3-BP are imparted on a variety of metabolic target molecules, including transporters, metabolic enzymes, and several other crucial stakeholders of tumor metabolism. Moreover, 3-BP ushers a reconstitution of the tumor microenvironment, a reversal of tumor acidosis, and recuperative action on vital organs and systems of the tumor-bearing host. Studies have been conducted to identify targets of 3-BP and its derivatives and characterization of target binding for further optimization. This review presents a brief and comprehensive discussion about the current state of knowledge concerning various aspects of tumor metabolism and explores the prospects of 3-BP as a safe and effective antineoplastic agent.

Dietary Omega-3 Polyunsaturated Fatty Acids Suppress NHE-1 Upregulation in a Rabbit Model of Volume- and Pressure-Overload

BACKGROUND

Increased consumption of omega-3 polyunsaturated fatty acids (ω3-PUFAs) from fish oil (FO) may have cardioprotective effects during ischemia/reperfusion, hypertrophy, and heart failure (HF). The cardiac Na(+)/H(+)-exchanger (NHE-1) is a key mediator for these detrimental cardiac conditions. Consequently, chronic NHE-1 inhibition appears to be a promising pharmacological tool for prevention and treatment. Acute application of the FO ω3-PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) inhibit the NHE-1 in isolated cardiomyocytes. We studied the effects of a diet enriched with ω3-PUFAs on the NHE-1 activity in healthy rabbits and in a rabbit model of HF induced by volume- and pressure-overload.

METHODS

Rabbits were allocated to four groups. The first two groups consisted of healthy rabbits, which were fed either a diet containing 1.25% (w/w) FO (ω3-PUFAs), or 1.25% high-oleic sunflower oil (ω9-MUFAs) as control. The second two groups were also allocated to either a diet containing ω3-PUFAs or ω9-MUFAs, but underwent volume- and pressure-overload to induce HF. Ventricular myocytes were isolated by enzymatic dissociation and used for intracellular pH (pH(i)) and patch-clamp measurements. NHE-1 activity was measured in HEPES-buffered conditions as recovery rate from acidosis due to ammonium prepulses.

RESULTS

In healthy rabbits, NHE-1 activity in ω9-MUFAs and ω3-PUFAs myocytes was not significantly different. Volume- and pressure-overload in rabbits increased the NHE-1 activity in ω9-MUFAs myocytes, but not in ω3-PUFAs myocytes, resulting in a significantly lower NHE-1 activity in myocytes of ω3-PUFA fed HF rabbits. The susceptibility to induced delayed afterdepolarizations (DADs), a cellular mechanism of arrhythmias, was lower in myocytes of HF animals fed ω3-PUFAs compared to myocytes of HF animals fed ω9-MUFAs. In our rabbit HF model, the degree of hypertrophy was similar in the ω3-PUFAs group compared to the ω9-MUFAs group.

CONCLUSION

Dietary ω3-PUFAs from FO suppress upregulation of the NHE-1 activity and lower the incidence of DADs in our rabbit model of volume- and pressure-overload.

Activation of a PAK-MEK signalling pathway in malaria parasite-infected erythrocytes

Merozoites of malaria parasites invade red blood cells (RBCs), where they multiply by schizogony, undergoing development through ring, trophozoite and schizont stages that are responsible for malaria pathogenesis. Here, we report that a protein kinase-mediated signalling pathway involving host RBC PAK1 and MEK1, which do not have orthologues in the Plasmodium kinome, is selectively stimulated in Plasmodium falciparum-infected (versus uninfected) RBCs, as determined by the use of phospho-specific antibodies directed against the activated forms of these enzymes. Pharmacological interference with host MEK and PAK function using highly specific allosteric inhibitors in their known cellular IC50 ranges results in parasite death. Furthermore, MEK inhibitors have parasiticidal effects in vitro on hepatocyte and erythrocyte stages of the rodent malaria parasite Plasmodium berghei, indicating conservation of this subversive strategy in malaria parasites. These findings have profound implications for the development of novel strategies for antimalarial chemotherapy.

Inhibition of Na(+)/H(+) exchanger 1 by 5-(N-ethyl-N-isopropyl) amiloride reduces hypoxia-induced hepatocellular carcinoma invasion and motility

Na(+)/H(+) exchanger 1 (NHE1) plays a significant role in tumor metastasis. However, the exact mechanisms by which NHE1 mediates cell invasion and migration, especially in hepatocellular carcinoma (HCC), are not yet known. In the current study, we show for the first time that the inhibition of NHE1 by 5-(N-ethyl-N-isopropyl) amiloride (EIPA) is able to suppress migration and invasion of HepG2 cells under hypoxic conditions. In addition, hypoxia activated ERK1/2, which in turn promoted the production of MMP-2, MMP-9 and VEGF. EIPA's suppressive role was determined to act through down-regulation of MMP-2, MMP-9 and VEGF in an ERK1/2 dependent manner. The data demonstrate that NHE1 plays a role in HCC invasion and that NHE1 may be a potential therapeutic target for HCC treatment.

Effects of rosiglitazone on plasma brain natriuretic peptide levels and myocardial performance index in patients with type 2 diabetes mellitus

Thiazolidinediones (TZD) have become a powerful tool for lowering insulin resistance. The problem of cardiovascular adverse events including fluid retention and risk of heart failure should be well known and recognised. We aimed to evaluate the long-term effects of rosiglitazone on cardiac function and fluid dynamics. Forty-six type 2 diabetic patients were randomised to treatment with rosiglitazone or metformin or to a control group. There are no significant differences between the groups in the duration of diabetes, HbA1c, plasma brain natriuretic peptide (BNP) levels, body mass index and myocardial performance indexes (MPIs) before the treatment. After three and six months all these parameters were repeated. Rosiglitazone increased plasma BNP levels and worsened MPIs 3 months after the start of treatment. Also left ventricular end-systolic volume increased and weight gain was observed. But these results were statistically non-significant (all p>0.05). When we continued rosiglitazone treatment to six months the increase in BNP levels became soft and statistically significant improvements were seen in MPIs (p<0.01). Also left ventricular end-systolic volume decreased significantly (p=0.004) and weight gain was stopped. In patients with type 2 diabetes, TZD treatment might have slight adverse effects on ventricular contractility and fluid dynamics at the beginning of the therapy. However, these changes seem to stabilise in the long term.

Antimalarial drug discovery: targeting protein kinases

Protein kinases (PKs) are prime targets for drug discovery in a variety of diseases, including cancer and neurodegenerative pathologies. The characterisation of the kinome of the human malaria parasite Plasmodium falciparum has revealed profound divergences, at several levels, between PKs of the parasite and those of its host. Here, the authors review the major issues and recent advances regarding the development of Plasmodium-selective PK inhibitors, with emphasis on target identification and validation, and on structure-based design. The authors also discuss the possibility of interfering with: i) Plasmodium PKs regulating transmission to the mosquito vector; and ii) host PKs that may be required for parasite survival.

Inhibition of the Na+-H+ exchanger isoform-1 and the extracellular signal-regulated kinase induces apoptosis: a time course of events

AIMS

The present study attempts to shed light on the role and the relative position of the Na(+)/H(+) exchanger isoform 1 (NHE1) and the extracellular signal-regulated kinase (ERK) in HEp-2 cell signaling pathways concerning a diverse range of cellular functions such as regulation of intracellular pH (pHi), DNA synthesis, production of reactive oxygen species (ROS) and apoptosis.

METHODS

Pharmacological inhibition with cariporide (highly specific inhibitor of NHE1) and PD98059 (specific inhibitor of the upstream activator of ERK) was implemented. Fluorescence spectrometry, atomic absorption spectrometry and ELISA methods were used in order to obtain the results.

RESULTS

NHE1 and ERK take part in all of the aforementioned cellular functions, as their inhibition had an effect on all of them. Additionally, inhibition of NHE1 resulted in ERK inhibition as well. Moreover, continuous inhibition of NHE1 or ERK for up to 24h led HEp-2 cells to apoptosis, as assessed through caspase-3 activation, DNA fragmentation and annexin-V binding levels.

CONCLUSION

Our data shows a time course of events in relation to NHE1 and ERK and suggests the existence of a positive feedback loop between NHE1 and ERK which could pose a barrier against apoptosis.

Protein kinases as targets for antimalarial intervention: Kinomics, structure-based design, transmission-blockade, and targeting host cell enzymes

The surge of interest in protein kinases as targets for chemotherapeutic intervention in a number of diseases such as cancer and neurodegenerative disorders has stimulated research aimed at determining whether enzymes of this class might also be considered as targets in the context of diseases caused by parasitic protists. Here, we present an overview of recent developments in this field, concentrating (i) on the benefits gained from the availability of genomic databases for a number of parasitic protozoa, (ii) on the emerging field of structure-aided design of inhibitors targeting protein kinases of parasitic protists, (iii) on the concept known as transmission-blockade, whereby kinases implicated in the development of the parasite in their arthropod vector might be targeted to interfere with disease transmission, and (iv) on the possibility of controlling parasitic diseases through the inhibition of host cell protein kinases that are required for the establishment of infection by the parasites.

Regulation of Na+/Mg2+ antiport in rat erythrocytes

In rat erythrocytes, the regulation of Na+/Mg2+ antiport by protein kinases (PKs), protein phosphatases (PPs), intracellular Mg2+, ATP and Cl- was investigated. In untreated erythrocytes, Na+/Mg2+ antiport was slightly inhibited by the PK inhibitor staurosporine, slightly stimulated by the PP inhibitor calyculin A and strongly stimulated by vanadate. PMA stimulated Na+/Mg2+ antiport. This effect was completely inhibited by staurosporine and partially inhibited by the PKC inhibitors Ro-31-8425 and BIM I. Participation of other PKs such as PKA, the MAPK cascade, PTK, CK I, CK II, CAM II-K, PI 3-K, and MLCK was excluded by use of inhibitors. Na+/Mg2+ antiport in rat erythrocytes can thus be stimulated by PKCalpha. In non-Mg2+ -loaded erythrocytes, ATP depletion reduced Mg2+ efflux and PMA stimulation in NaCl medium. A drastic activation of Na+/Mg2+ antiport was induced by Mg2+ loading which was not further stimulated by PMA. Staurosporine, Ro-31-8425, BIM I and calyculin A did not inhibit Na+/Mg2+ antiport of Mg2+ -loaded cells. Obviously, at high [Mg2+]i Na+/Mg2+ antiport is maximally stimulated. PKCalpha or PPs are not involved in stimulation by intracellular Mg2+. ATP depletion of Mg2+ -loaded erythrocytes reduced Mg2+ efflux and the affinity of Mg2+ binding sites of the Na+/Mg2+ antiporter to Mg2+. In non-Mg2+ -loaded erythrocytes Na+/Mg2+ antiport essentially depends on Cl-. Mg2+ -loaded erythrocytes were less sensitive to the activation of Na+/Mg2+ antiport by [Cl-]i.

Cytosolic phospholipase A2 type IVA is present in human red cells

Phospholipase A(2) type IVA (IVAPLA(2)) is a cytosolic enzyme that on activation selectively releases arachidonic acid (AA) from cell membrane phospholipids. Both AA and lysophospholipid, products of the enzymic reaction, can function as signal transducers in cellular interactions. The enzyme is present in most cells, including polymorphs, eosinophils, and platelets. This study used affinity purification to extract IVAPLA(2) from red cell lysate prepared from leukocyte- and platelet-depleted human blood to overcome the masking effect of hemoglobin on Western blot detection. We show that IVAPLA(2) is present in red cells as a 90-kDa protein.

ERK Is Regulated by Sodium-Proton Exchanger in Rat Aortic Vascular Smooth Muscle Cells

The purposes of this study were to test 1) the relationship between two widely studied mitogenic effector pathways, and 2) the hypothesis that sodium-proton exchanger type 1 (NHE-1) is a regulator of extracellular signal-regulated protein kinase (ERK) activation in rat aortic smooth muscle (RASM) cells. Angiotensin II (Ang II) and 5-hydroxytryptamine (5-HT) stimulated both ERK and NHE-1 activities, with activation of NHE-1 preceding that of ERK. The concentration-response curves for 5-HT and Ang II were superimposable for both processes. Inhibition of NHE-1 with pharmacological agents or by isotonic replacement of sodium in the perfusate with choline or tetramethylammonium greatly attenuated ERK activation by 5-HT or Ang II. Similar maneuvers significantly attenuated 5-HT- or Ang II-mediated activation of MEK and Ras but not transphosphorylation of the epidermal growth factor (EGF) receptor. EGF receptor blockade attenuated ERK activation, but not NHE-1 activation by 5-HT and Ang II, suggesting that the EGF receptor and NHE-1 work in parallel to stimulate ERK activity in RASM cells, converging distal to the EGF receptor but at or above the level of Ras in the Ras-MEK-ERK pathway. Receptor-independent activation of NHE-1 by acute acid loading of RASM cells resulted in the rapid phosphorylation of ERK, which could be blocked by pharmacological inhibitors of NHE-1 or by isotonic replacement of sodium, closely linking the proton transport function of NHE-1 to ERK activation. These studies identify NHE as a new regulator of ERK activity in RASM cells.

Troglitazone reduces activity of the Na+/H+ exchanger in fructose-fed borderline hypertensive rats

Activation of the Na+/H+ exchanger (NHE) is known to be related to elevated blood pressure in hyperinsulinemia. We previously demonstrated that a fructose-enriched diet induced hyperinsulinemia and hypertriglyceridemia, elevated NHE activity, increased intracellular calcium concentrations ([Ca2+]i), and increased blood pressure in borderline hypertensive rats (BHR). This study examines whether pharmacologically reducing plasma triglyceride or insulin concentrations lowers blood pressure and reduces NHE activity in fructose-fed BHR. Eicosapentaenoic acid (EPA), bezafibrate (BEZ), and troglitazone (TRO) were administered to treat hypertriglyceridemia and/or hyperinsulinemia. Rats were fed a 60% fructose diet or a control diet for 4 weeks, followed by a diet with either vehicle, EPA, BEZ, or TRO for 4 weeks. Intracellular pH (pHi) was measured in platelets by fluorescent dye. Platelet NHE activity was evaluated by the recovery of pHi following addition of sodium propionate (Vmax). [Ca2+]i in platelets were measured fluorometrically. In fructose-fed rats, EPA prevented further increase in blood pressure, and reduced triglyceride concentration and [Ca2+]i without affecting Vmax or plasma insulin concentrations. BEZ reduced triglyceride concentrations without affecting blood pressure, Vmax, [Ca2+]i, or insulin concentrations. TRO prevented an increase in blood pressure, and reduced Vmax, [Ca2+]i, and insulin, but not triglycerides. Plasma insulin and Vmax were positively correlated. In conclusion, improvement of hyperinsulinemia can decrease NHE activity and blood pressure in fructose-fed BHR.

Effect of protein kinase C activation on Na+-H+ exchange in erythrocytes of frog Rana temporaria

The treatment of frog erythrocytes incubated in standard nitrate medium with 100 nM phorbol ester (PMA) induced a sharp increase in the 22Na uptake by the cells and intracellular Na(+) concentration. The PMA-induced enhancement in 22Na uptake was stimulated by the addition of 0.1 mM ouabain to the incubation medium and completely blocked by 1 mM amiloride. The time course of 22Na uptake by frog red cells in the presence of PMA showed a lag phase ( approximately 5 min), after which was linear within 5-15 min. The calculated Na(+) influx in erythrocytes treated with PMA was 49.4+/-3.7 mmol l(-1) cells h(-1) as compared with 1.2+/-0.25 mmol l(-1) h(-1) for control cells. 5-(N-ethyl-N-isopropyl)-amiloride, selective blocker of NHE1, caused a dose-dependent inhibition of the PMA-induced Na(+) influx with IC(50) of 0.27 microM. The PMA-induced Na(+) influx was almost completely inhibited by 0.1 microM staurosporine, protein kinase C blocker. Pretreatment of frog red blood cells for 5, 10 or 15 min with 10 mM NaF, non-selective inhibitor of protein phosphatase, led to a progressive stimulation of the PMA effect on Na(+) influx. Both amiloride and NaF did not affect the basal Na(+) influx in frog erythrocytes. The data indicate that the Na(+)-H(+) exchanger in the frog erythrocytes is quiescent under basal conditions and can be markedly stimulated by PMA.

Hypertension and insulin disorders

Insulin resistance and/or compensatory hyperinsulinemia are associated with hypertension, obesity, dyslipidemia, and glucose intolerance. Insulin resistance and hyperinsulinemia are considered to increase blood pressure through sympathetic nervous system activation, renin-angiotensin system stimulation, and vascular smooth muscle cell proliferation. Leptin, magnesium ions, nitric oxide, endothelin, peroxisome proliferator-activated receptor gamma, and tumor necrosis factor-alpha also modulate blood pressure. Decreasing insulin resistance by lifestyle modification including diet, weight loss, and physical exercise has been shown to reduce blood pressure. Angiotensin-converting enzyme inhibitors have a beneficial effect on insulin resistance. On the other hand, the angiotensin II antagonist, losartan, does not affect insulin sensitivity. The selective alpha1-blockers have a favorable metabolic profile producing increases in insulin sensitivity. A short-acting type calcium channel blocker seems to decrease insulin sensitivity. On the other hand, long-acting type calcium channel blockers improve insulin sensitivity. Thiazide diuretics and most of the beta-blockers decrease insulin sensitivity. Vasodilatory beta-blockers have been reported to improve insulin sensitivity. Use of low-dose diuretics avoids the adverse effects seen with conventional doses.

Comparison of the mechanisms of nongenomic actions of thyroid hormone and steroid hormones

Steroids and thyroid hormone are thought primarily to act via binding to hormone-specific nuclear receptor superfamily members. The nuclear ligand-receptor complexes then initiate transcriptional activity. Actions of steroids and iodothyronines that are nongenomic or extranuclear in mechanism have been recognized recently and new insights into such mechanisms are available. Despite their distinct structures and biologic effects, the two families of hormones have similarities in the mechanisms of their nongenomic actions. That is, both steroids and thyroid hormone appear to interact with specific cell surface G protein-coupled receptors and to activate signal transducing kinases such as those involved in the mitogen-activated protein kinase (MAPK) pathway. Much is known about the ability of certain steroids such as estrogen and mineralocorticoids to increase [Ca2+]i acutely and stimulation of the MAPK cascade by L-T4 appears to depend upon a hormone-induced increase in [Ca2+]i via phosphoinositide pathway activation. At least in the case of iodothyronines, hormone activation of the MAPK pathway modulates the cellular activities of certain cytokines and growth factors. One of the two cell surface estrogen receptors (ERs) may be an expression of the same transcript as that for nuclear ER, whereas the mineralocorticoid and progesterone-binding proteins in the plasma membrane appear to be products of genes different from those of nuclear receptors. Iodothyronine structure-activity relationships at the plasma membrane binding site for thyroid hormone suggest that the cell surface receptor for T4 that also binds 3,5,3'-triiodo-L-T3 is different from the nuclear T3 receptor (TR). There are interfaces of nongenomic and genomic mechanisms for both steroids and thyroid hormone. For example, by nongenomic mechanisms, estrogen and thyroid hormone can promote serine phosphorylation, respectively, of nuclear ER and TR. Transcriptional activity of the nuclear receptor proteins can be altered by such phosphorylation.

The effect of leptin on Na(+)-H(+) antiport (NHE 1) activity of obese and normal subjects erythrocytes

Obesity is currently considered as a chronic metabolic disease, associated with a high risk of cardiovascular complications. Leptin, an adipocyte-derived hormone has a variety target cells influencing a wide range of processes. Possible counteractions of hyperleptinaemia are currently investigated. The Na(+)-H(+) exchanger (NHE 1) is involved in multiple cellular functions and its activation has been related to hypertension and obesity. NHE 1 is present on erythrocytes and can be stimulated by various hormones. Erythrocytes have on their surface a variety of receptors with mostly unknown function. In the present paper, the effect of leptin on erythrocytes NHE 1 activity has been investigated. For this reason, the intracellular pH and sodium influxes were measured before and after addition of leptin in erythrocyte suspensions from normal and obese individuals. Amiloride, a specific NHE 1 inhibitor, and staurosporine a protein kinase C inhibitor were used to inhibit erythrocyte NHE 1. For the binding study leptin was labeled with fluorescein isothiocyanate (FITC) and the binding on erythrocytes was estimated by Scatchard analysis. NHE 1 activity increased in the presence of leptin but significantly less in the obese than in the control group. Furthermore the concentrations of leptin binding sites on the surface of erythrocytes were lower in erythrocytes drawn from obese individuals than in erythrocytes drawn from normal subjects. Since NHE 1 activity has been associated with insulin resistance and hypertension, the activation of this antiport by leptin may represent a link between adipose tissue hypertrophy and cardiovascular complications of obesity.

Adrenomedullin stimulates DNA synthesis of rat adrenal zona glomerulosa cells through activation of the mitogen-activated protein kinase-dependent cascade

BACKGROUND

Adrenal zona glomerulosa cells are provided with adrenomedullin receptors. Adrenomedullin has recently been found to enhance proliferation of cultured rat vascular smooth muscle cells and zona glomerulosa cells.

OBJECTIVE

To investigate whether adrenomedullin affects rat zona glomerulosa proliferative activity through the tyrosine kinase and extracellular signal regulated kinases (ERKs) pathways.

METHODS

Dispersed rat zona glomerulosa cells were cultured in vitro for 24 h and then exposed to adrenomedullin (10(-7) mol/l), alone or in the presence of tyrphostin-23 (10(-5) mol/l) or PD-98059 (10(-4) mol/l), for 24 or 48 h. To assess the rate of DNA synthesis, 5-bromo-2'-deoxyuridine (BrdU, 20 mg/ml) was also added to the medium and BrdU-positive cells were detected by immunocytochemistry. The expression of ERKs and the effect of adrenomedullin on ERKs phosphorylation and activity were assayed in dispersed zona glomerulosa cells.

RESULTS

Adrenomedullin significantly increased the percentage of BrdU-positive (phase-S) zona glomerulosa cells; this effect was blocked by either the tyrosine kinase inhibitor, tyrphostin-23, or the mitogen-activated protein kinase kinase (MEK-1) inhibitor, PD-98059. Both zona glomerulosa and zona fasciculata/reticularis express ERK-1 (44 kDa) and ERK-2 (42 kDa) isoforms. However, adrenomedullin phosphorylated ERK-1 and ERK-2 only in the zona glomerulosa; this effect was blunted by the MEK-1 inhibitor, PD98059, and by the calcitonin gene-related peptide type 1 (CGRP-1) receptor antagonist, CGRP8-37, but not by the adrenomedullin C-terminal fragment, ADM22-52.

CONCLUSION

Adrenomedullin stimulates the growth of rat zona glomerulosa cells through activation of CGRP-1 receptor, linked to the tyrosine kinase-MEK-1-ERKs signalling pathway. These results confirm the complex role played by this peptide in the regulation of zona glomerulosa cell physiology.

Presence of a Na(+)/H(+) exchanger in acidocalcisomes of Leishmania donovani and their alkalization by anti-leishmanial drugs

Acidocalcisomes are acidic vacuoles present in trypanosomatids that contain most of the cellular calcium. The data presented here demonstrate that Leishmania donovani acidocalcisomes possess a Na(+)/H(+) exchanger. 3,5-Dibutyl-4-hydroxytoluene, in the concentration range of 0-20 microM, inhibited the Na(+)/H(+) exchanger, and strongly stimulated the activity of the vacuolar H(+)-ATPase responsible for vacuolar acidification. As occurs with Na(+), the cationic anti-leishmanial drugs pentamidine, WR-6026, and chloroquine promoted a fast and extensive alkalization of the L. donovani acidocalcisomes.