Expression and regulation of the Na(+)/K(+)/2Cl(-) cotransporter NKCC1 in rat liver and human HuH-7 hepatoma cells

Cation-Chloride Cotransporters KCC2 and NKCC1 as Therapeutic Targets in Neurological and Neuropsychiatric Disorders

Neurological diseases including Alzheimer's, Huntington's disease, Parkinson's disease, Down syndrome and epilepsy, and neuropsychiatric disorders such as schizophrenia, are conditions that affect not only individuals but societies on a global scale. Current therapies offer a means for small symptomatic relief, but recently there has been increasing demand for therapeutic alternatives. The γ-aminobutyric acid (GABA)ergic signaling system has been investigated for developing new therapies as it has been noted that any dysfunction or changes to this system can contribute to disease progression. Expression of the K-Cl-2 (KCC2) and N-K-C1-1 (NKCC1) cation-chloride cotransporters (CCCs) has recently been linked to the disruption of GABAergic activity by affecting the polarity of GABA_A receptor signaling. KCC2 and NKCC1 play a part in multiple neurological and neuropsychiatric disorders, making them a target of interest for potential therapies. This review explores current research suggesting the pathophysiological role and therapeutic importance of KCC2 and NKCC1 in neuropsychiatric and neurological disorders.

Beta-Amyloid (Aβ1-42) Increases the Expression of NKCC1 in the Mouse Hippocampus

Alzheimer’s disease (AD) is a neurodegenerative disorder with an increasing need for developing disease-modifying treatments as current therapies only provide marginal symptomatic relief. Recent evidence suggests the γ-aminobutyric acid (GABA) neurotransmitter system undergoes remodeling in AD, disrupting the excitatory/inhibitory (E/I) balance in the brain. Altered expression levels of K-Cl-2 (KCC2) and N-K-Cl-1 (NKCC1), which are cation–chloride cotransporters (CCCs), have been implicated in disrupting GABAergic activity by regulating GABA_A receptor signaling polarity in several neurological disorders, but these have not yet been explored in AD. NKCC1 and KCC2 regulate intracellular chloride [Cl⁻]_i by accumulating and extruding Cl⁻, respectively. Increased NKCC1 expression in mature neurons has been reported in these disease conditions, and bumetanide, an NKCC1 inhibitor, is suggested to show potential therapeutic benefits. This study used primary mouse hippocampal neurons to explore if KCC2 and NKCC1 expression levels are altered following beta-amyloid (Aβ_1-42) treatment and the potential neuroprotective effects of bumetanide. KCC2 and NKCC1 expression levels were also examined in 18-months-old male C57BL/6 mice following bilateral hippocampal Aβ_1-42 stereotaxic injection. No change in KCC2 and NKCC1 expression levels were observed in mouse hippocampal neurons treated with 1 nM Aβ_1-42, but NKCC1 expression increased 30-days post-Aβ_1-42-injection in the CA1 region of the mouse hippocampus. Primary mouse hippocampal cultures were treated with 1 nM Aβ_1-42 alone or with various concentrations of bumetanide (1 µM, 10 µM, 100 µM, 1 mM) to investigate the effect of the drug on cell viability. Aβ_1-42 produced 53.1 ± 1.4% cell death after 5 days, and the addition of bumetanide did not reduce this. However, the drug at all concentrations significantly reduced cell viability, suggesting bumetanide is highly neurotoxic. In summary, these results suggest that chronic exposure to Aβ_1-42 alters the balance of KCC2 and NKCC1 expression in a region-and layer-specific manner in mouse hippocampal tissue; therefore, this process most likely contributes to altered hippocampal E/I balance in this model. Furthermore, bumetanide induces hippocampal neurotoxicity, thus questioning its suitability for AD therapy. Further investigations are required to examine the effects of Aβ_1-42 on KCC2 and NKCC1 expression and whether targeting CCCs might offer a therapeutic approach for AD.

Treatment experience in two adults with creatinfe transporter deficiency

Background

Creatine transporter deficiency (CTD) is an X-linked form of intellectual disability (ID) caused by SCL6A8 mutations. Limited information exists on the adult course of CTD, and there are no treatment studies in adults.

Methods

We report two half-brothers with CTD, 36 and 31 years at intervention start. Their clinical phenotypes were consistent with CTD, and intervention was indicated because of progressive disease course, with increased difficulties speaking, walking and eating, resulting in fatigue, and malnutrition. We therefore performed treatment trials with arginine, glycine and a proprietary product containing creatine and betaine, and then a trial supplementing with betaine alone.

Results

In the older patient, glycine and arginine were accompanied by adverse effects, while betaine containing proprietary product gave improved balance, speech and feeding. When supplementation stopped, his condition deteriorated, and improved again after starting betaine supplement. Betaine supplementation was also beneficial in the younger patient, reducing his exhaustion, feeding difficulties and weight loss, making him able to resume his protected work.

Discussion & conclusion

We report for the first time that betaine supplement was well tolerated and efficient in adults with CTD, while arginine and/or glycine were accompanied by side effects. Thus, betaine is potentially a new useful treatment for CTD patients. We discuss possible underlying treatment mechanisms. Betaine has been reported to have antagonistic effect on NKCC1 channels, a mechanism shared with bumetanide, a medication with promising results in both in autism and epilepsy. Further studies of betaine's effects in well-designed studies are warranted.

Sodium homeostasis in the tumour microenvironment

The concentration of sodium ions (Na+) is raised in solid tumours and can be measured at the cellular, tissue and patient levels. At the cellular level, the Na+ gradient across the membrane powers the transport of H+ ions and essential nutrients for normal activity. The maintenance of the Na+ gradient requires a large proportion of the cell's ATP. Na+ is a major contributor to the osmolarity of the tumour microenvironment, which affects cell volume and metabolism as well as immune function. Here, we review evidence indicating that Na+ handling is altered in tumours, explore our current understanding of the mechanisms that may underlie these alterations and consider the potential consequences for cancer progression. Dysregulated Na+ balance in tumours may open opportunities for new imaging biomarkers and re-purposing of drugs for treatment.

Solute carrier transporters: potential targets for digestive system neoplasms

Digestive system neoplasms are the leading causes of cancer-related death all over the world. Solute carrier (SLC) superfamily is composed of a series of transporters that are ubiquitously expressed in organs and tissues of digestive systems and mediate specific uptake of small molecule substrates in facilitative manner. Given the important role of SLC proteins in maintaining normal functions of digestive system, dysregulation of these protein in digestive system neoplasms may deliver biological and clinical significance that deserves systemic studies. In this review, we critically summarized the recent advances in understanding the role of SLC proteins in digestive system neoplasms. We highlighted that several SLC subfamilies, including metal ion transporters, transporters of glucose and other sugars, transporters of urea, neurotransmitters and biogenic amines, ammonium and choline, inorganic cation/anion transporters, transporters of nucleotide, amino acid and oligopeptide organic anion transporters, transporters of vitamins and cofactors and mitochondrial carrier, may play important roles in mediating the initiation, progression, metastasis, and chemoresistance of digestive system neoplasms. Proteins in these SLC subfamilies may also have diagnostic and prognostic values to particular cancer types. Differential expression of SLC proteins in tumors of digestive system was analyzed by extracting data from human cancer database, which revealed that the roles of SLC proteins may either be dependent on the substrates they transport or be tissue specific. In addition, small molecule modulators that pharmacologically regulate the functions of SLC proteins were discussed for their possible application in the treatment of digestive system neoplasms. This review highlighted the potential of SLC family proteins as drug target for the treatment of digestive system neoplasms.

Discovery of NKCC1 as a potential therapeutic target to inhibit hepatocellular carcinoma cell growth and metastasis

Metastasis is the essential cause for the high mortality of hepatocellular carcinoma (HCC). In order to investigate the mechanism of metastasis, and to discover therapeutic targets for HCC, the quantitative proteomic technique was applied to characterize the plasma membrane proteins of two HCC cell lines with low (MHCC97L) or high (MHCC97H) metastatic potentials. One of the plasma membrane proteins, sodium-potassium-chloride cotransporter 1 (NKCC1), was upregulated in MHCC97H cell line. Immunohistochemistry result in HCC patients showed that NKCC1 expression was associated with poor differentiation and microvascular invasion. Knockdown of NKCC1 via RNA interference reduced HCC cell proliferation and invasion abilities in vitro and in vivo, whereas over-expression of NKCC1 significantly increased HCC cell proliferation and invasion abilities in vitro and in vivo. Additionally, blocking NKCC1 activity with bumetanide attenuated the proliferation and invasion abilities of HCC cells in vitro and limited the HCC growth in vivo. Further results suggested that NKCC1 promotes the invasion ability via MMP-2 activity, and that the WNK1/OSR1/NKCC1 signal pathway might play roles in HCC metastasis. For the first time, our study demonstrated that NKCC1 plays a role in HCC metastasis, and could be served as a potential target to inhibit HCC cell growth and metastasis.

Molecular physiology of SPAK and OSR1: two Ste20-related protein kinases regulating ion transport

SPAK (Ste20-related proline alanine rich kinase) and OSR1 (oxidative stress responsive kinase) are members of the germinal center kinase VI subfamily of the mammalian Ste20 (Sterile20)-related protein kinase family. Although there are 30 enzymes in this protein kinase family, their conservation across the fungi, plant, and animal kingdom confirms their evolutionary importance. Already, a large volume of work has accumulated on the tissue distribution, binding partners, signaling cascades, and physiological roles of mammalian SPAK and OSR1 in multiple organ systems. After reviewing this basic information, we will examine newer studies that demonstrate the pathophysiological consequences to SPAK and/or OSR1 disruption, discuss the development and analysis of genetically engineered mouse models, and address the possible role these serine/threonine kinases might have in cancer proliferation and migration.

The role of hyperosmotic stress in inflammation and disease

Hyperosmotic stress is an often overlooked process that potentially contributes to a number of human diseases. Whereas renal hyperosmolarity is a well-studied phenomenon, recent research provides evidence that many non-renal tissues routinely experience hyperosmotic stress that may contribute significantly to disease initiation and progression. Moreover, a growing body of evidence implicates hyperosmotic stress as a potent inflammatory stimulus by triggering proinflammatory cytokine release and inflammation. Under physiological conditions, the urine concentrating mechanism within the inner medullary region of the mammalian kidney exposes cells to high extracellular osmolarity. As such, renal cells have developed many adaptive strategies to compensate for increased osmolarity. Hyperosmotic stress is linked to many maladies, including acute and chronic, as well as local and systemic, inflammatory disorders. Hyperosmolarity triggers cell shrinkage, oxidative stress, protein carbonylation, mitochondrial depolarization, DNA damage, and cell cycle arrest, thus rendering cells susceptible to apoptosis. However, many adaptive mechanisms exist to counter the deleterious effects of hyperosmotic stress, including cytoskeletal rearrangement and up-regulation of antioxidant enzymes, transporters, and heat shock proteins. Osmolyte synthesis is also up-regulated and many of these compounds have been shown to reduce inflammation. The cytoprotective mechanisms and associated regulatory pathways that accompany the renal response to hyperosmolarity are found in many non-renal tissues, suggesting cells are commonly confronted with hyperosmotic conditions. Osmoadaptation allows cells to survive and function under potentially cytotoxic conditions. This review covers the pathological consequences of hyperosmotic stress in relation to disease and emphasizes the importance of considering hyperosmolarity in inflammation and disease progression.

Cytoprotective role of mitogen-activated protein kinase phosphatase-1 in light-damaged human retinal pigment epithelial cells

The role of the mitogen-activated protein (MAP) kinase phosphatases (MKPs) in light-damaged cells is unclear. Therefore we investigated the involvement of MKP-1 in the regulation of apoptosis and cell survival mediated by MAP kinase pathways in light-damaged human retinal pigment epithelial cells (ARPE-19). Light dose-dependent changes in the expression of MKP-1 and in the phosphorylation status of the MAP kinases, c-Jun-N-terminal kinase (JNK) and p38 were demonstrated. Low light doses up to 2 J cm(-2) led to an upregulation of MKP-1 which resulted in the prevention of cell death by inactivating JNK kinase. However, higher light doses (> or =3 J cm(-2)) significantly reduced MKP-1 protein expression and subsequently led to an increased JNK kinase activity followed by a significant increase in cell death. JNK kinase inactivation by the JNK inhibitor SP600125 significantly reduced light-induced cell death, suggesting that the cytoprotective properties of MKP-1 are mediated mainly by the JNK MAP kinase pathway. Physiological concentrations of ascorbic acid or taurine were seen to prevent apoptosis and cell death in light-damaged ARPE-19 cells by reducing oxidative stress within cells, thus maintaining MKP-1 at high levels, leading to an inactivation of the JNK kinase pathway which resulted in an increased cell viability.

Extracellular glutamine is a critical modulator for regulatory volume increase in human glioma cells

Mammalian cells regulate their volume to prevent unintentional changes in intracellular signaling, cell metabolism, and DNA integrity. Intentional cell volume changes occur as cells undergo proliferation, apoptosis, or cell migration. To regulate cell volume, cells use channels and transport systems to flux osmolytes across the plasma membrane followed by the obligatory movement of water. While essentially all cells are capable of regulatory volume decrease (RVD), regulatory volume increase (RVI) mechanisms have only been reported in some cell types. In this investigation, we used human glioma cells as a model system to determine conditions necessary for RVI. When exposed to hyperosmotic conditions through the addition of 30 mosM NaCl or sucrose, D54-MG and U251 glioma cell lines and glioma cells from acute patient biopsies shrunk transiently but were able to fully recover their original cell volume within 40-70 min. This ability was highly temperature sensitive and absolutely required the presence of low millimolar concentrations of l-glutamine in the extracellular solution. Other known substrates of glutamine transporters such as methyl-amino isobutyric acid (MeAIB), alanine, and threonine were unable to support RVI. The ability of cells to undergo RVI also required the presence of Na+, K+, and Cl- and was inhibited by the NKCC inhibitor, bumetanide, consistent with the involvement of a Na+/K+/2Cl- cotransporter (NKCC). Moreover, the expression of NKCC1 was demonstrated by Western blot. We concluded that regulatory volume increase in human glioma cells occurs through the uptake of Na+, K+, and Cl- by NKCC1 and is modulated by the presence of glutamine.

Osmosensing by integrins in rat liver

Changes in hepatocyte hydration are induced not only by ambient hypo- or hyperosmolarity, but also under isosmotic condition by hormones, substrates, and oxidative stress. The perfused rat liver is a well-established intact organ model with preservation of the three-dimensional hepatocyte anchoring to the extracellular matrix and/or adjacent cells, parenchymal cell polarity, liver cell heterogeneity, acinar construction, and gene expression gradients. Originally, data from the perfused rat liver indicated that changes of cell hydration independent of their origin critically contribute to the control of autophagic proteolysis and canalicular bile acid excretion. Meanwhile, the concept that cell hydration changes trigger signal transduction processes that control metabolism, gene expression, transport, and the susceptibility to stress is well accepted. This chapter summarizes evidence obtained from experiments with the perfused rat liver that integrins are osmosensors in the liver and thereby critically contribute to the Src- and MAP-kinase-dependent inhibition of autophagic proteolysis, stimulation of canalicular taurocholate excretion, and regulatory volume decrease as induced by hypoosmotic swelling. Moreover, integrin-dependent sensing of hepatocyte swelling is essential for signaling and proteolysis inhibition by insulin and glutamine. These findings define a novel role of integrins in insulin and glutamine signaling and set an example for mechanotransduction as an integral part of overall growth factor and nutrient signaling.

Fate of hypertonicity-stressed corneal epithelial cells depends on differential MAPK activation and p38MAPK/Na-K-2Cl cotransporter1 interaction

The capacity of the corneal epithelium to adapt to hypertonic challenge is dependent on the ability of the cells to upregulate the expression and activity of cell membrane-associated Na-K-2Cl cotransporter1 (NKCC1). Yet, the signaling pathways that control this response during hypertonic stress are still unclear. We studied stress-induced changes in proliferation and survival capacity of SV40-immortalized human (HCEC) and rabbit (RCEC) corneal epithelial cells as a function of (i) the magnitude of the hypertonic challenge, (ii) differential changes in activation of mitogen-activated protein kinase (MAPK), and (iii) the extent of p38MAPK interaction with NKCC1. Cells were incubated in hypertonic (up to 600 mOsm) media for varying time periods up to 24 h. Phosphorylated forms of p44/42, p38, and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) MAPK were immunoprecipitated from cell lysates, and the amount of each activated NKCC1-associated MAPK was evaluated by Western blot/ECL assay. DNA integrity was assessed by electrophoresis in a 2% agarose gel. Cell survival and proliferation were evaluated based on three criteria: protein content, cell count, and the MTT assay. Exposure to media of 325-350 mOsm increased proliferation of HCEC up to 75%, whereas this response was limited to <16% in RCEC. At higher osmolarities, cell proliferation decreased in both species. SAPK/JNK activity increased 150-fold in HCEC and <10-fold in RCEC, while DNA fragmentation occurred only in HCEC. Compared to HCEC, the better RCEC survival rate was associated with higher p38MAPK activity and near complete restoration of p44/42MAPK activity after the first 30 min. In both cell lines, the amount of phospho-NKCC1 that coimmunoprecipitated with phospho-p38MAPK was proportional to the magnitudes of their respective activation levels. However, no such associations occurred between amounts of phosphorylated p44/42MAPK or SAPK/JNK and phospho-NKCC1. Under isotonic conditions, with bumetanide-induced inhibition of RCEC and HCEC NKCC1 activities, p44/42MAPK activity declined by 40 and 60%, respectively. Such declines led to proportional decreases in cell proliferation. Survival of hypertonicity-stressed corneal epithelial cells depends both on p38MAPK activation capacity and the ability of p38MAPK to stimulate NKCC1 activity through protein-protein interaction. The level of NKCC1 activation affects the extent of cell volume recovery and, in turn, epithelial survival capacity.

The role of the neutral amino acid transporter SNAT2 in cell volume regulation

Sodium-dependent neutral amino acid transporter-2 (SNAT2), the ubiquitous member of SLC38 family, accounts for the activity of transport system A for neutral amino acids in most mammalian tissues. As the transport process performed by SNAT2 is highly energized, system A substrates, such as glutamine, glycine, proline and alanine, reach high transmembrane gradients and constitute major components of the intracellular amino acid pool. Moreover, through a complex array of exchange fluxes, involving other amino acid transporters, and of metabolic reactions, such as the synthesis of glutamate from glutamine, SNAT2 activity influences the cell content of most amino acids, thus determining the overall size and the composition of the intracellular amino acid pool. As amino acids represent a large fraction of cell organic osmolytes, changes of SNAT2 activity are followed by modifications in both cell amino acids and cell volume. This mechanism is utilized by many cell types to perform an effective regulatory volume increase (RVI) upon hypertonic exposure. Under these conditions, the expression of SNAT2 gene is induced and newly synthesized SNAT2 proteins are preferentially targeted to the cell membrane, leading to a significant increase of system A transport Vmax. In cultured human fibroblasts incubated under hypertonic conditions, the specific silencing of SNAT2 expression, obtained with anti-SNAT2 siRNAs, prevents the increase in system A transport activity, hinders the expansion of intracellular amino acid pool, and significantly delays cell volume recovery. These results demonstrate the pivotal role played by SNAT2 induction in the short-term hypertonic RVI and suggest that neutral amino acids behave as compatible osmolytes in hypertonically stressed cells.

Cell hydration and mTOR-dependent signalling

Insulin- and amino acid-induced signalling by the mammalian target of rapamycin (mTOR) involves hyperphosphorylation of the p70 ribosomal S6 protein kinase (p70S6-kinase) and the eukaryotic initiation factor 4E (eIF4E) binding protein 4E-BP1 and contributes to regulation of protein metabolism. This review considers the impact of cell hydration on mTOR-dependent signalling. Although hypoosmotic hepatocyte swelling in some instances activates p70S6-kinase, the hypoosmolarity-induced proteolysis inhibition in perfused rat liver is insensitive to mTOR inhibition by rapamycin. Likewise, swelling-dependent proteolysis inhibition by insulin and swelling-independent proteolysis inhibition by leucine, a potent activator of p70S6-kinase and 4E-BP1 hyperphosphorylation, in perfused rat liver is insensitive to rapamycin, indicating that at least rapamycin-sensitive mTOR signalling is not involved. Hyperosmotic dehydration in different cell types produces inactivation of signalling components around mTOR, thereby attenuating insulin-induced glucose uptake, glycogen synthesis, and lipogenesis in adipocytes, and MAP-kinase phosphatase MKP-1 expression in hepatoma cells. Direct inactivation of mTOR, stimulation of the AMP-activated protein kinase, and the destabilization of individual proteins may impair mTOR signalling under dehydrating conditions. Further investigation of the crosstalk between the mTOR pathway(s) and hyperosmotic signalling will improve our understanding about the contribution of cell hydration changes in health and disease and will provide further rationale for fluid therapy of insulin-resistant states.

Oligonucleotide microarray analysis of differential transporter regulation in the regenerating rat liver

AIMS

The aim of this study was to investigate the regulation of hepatic transport systems during liver regeneration.

METHODS

A DNA oligonucleotide microarray was developed with probes for 400 transcripts. Data were confirmed using real-time PCR and on a functional level in the perfused rat liver. Liver homogenates were taken 3-48 h following 2/3-hepatectomy in rats and compared with sham-operated and non-operated controls.

RESULTS

A more than two-fold increase or decrease of expression was obtained in 183 genes following partial hepatectomy and in 16 genes in sham-operated rats. A strong induction during liver regeneration was detected for the amino acid transporters LAT4, SN2 and sodium-dependent neutral amino acid transporter (ASCT)2, whereas amino acid transport system (ATA)2 and ATA3 expressions remained unchanged. The upregulation of ASCT2 may be responsible for the increase in sodium-dependent neutral amino acid influx important for liver cell proliferation. Expression of the osmolyte transporters Smit, TauT and Bgt1 was almost unchanged indicating that osmolytes are not involved in the cell volume increase during liver regeneration. The basolateral bile salt transporter Ntcp messenger RNA (mRNA) was significantly downregulated, whereas bile salt export pump (Bsep) and multidrug resistance protein (Mrp)2 expressions remained almost unchanged. An increased mRNA expression following partial hepatectomy was detected for organic anion transporting polypeptide (Oatp)5, Octn1, Octn2 and SGLT2. In contrast, Mrp6, Oatp 2, Oatp 3, Oatp 4 and Oatp 7 were downregulated. A five-fold upregulation at the protein level was shown for the Na(+)-K(+)-2Cl- cotransporter sodium-potassium-2-chloride cotransporter (NKCC1).

CONCLUSIONS

The data show a differential regulation of hepatic transport systems during liver regeneration.

Expression of taurine transporter is regulated through the TonE (tonicity-responsive element)/TonEBP (TonE-binding protein) pathway and contributes to cytoprotection in HepG2 cells

In hypertonic environment, taurine accumulates in cells via activation of TauT (taurine transporter) as an adaptive regulation. Recent studies revealed that TonE (tonicity-responsive element)/TonEBP (TonE-binding protein) pathway regulated the expression of various molecules which protect cells against hypertonic stress. In the present study, we investigated the osmoregulatory mechanisms of TauT expression. TauT was up-regulated at both functional and transcriptional levels in HepG2 under hypertonic condition. The TonE site was identified in the promoter region of TauT gene. Reporter gene assay revealed that promoter activity was increased under hypertonic conditions, whereas deletion or mutation of TonE sequence abolished the induction of the promoter activity in response to hypertonicity. By using the reporter gene plasmids containing a TonE site of TauT promoter (p2xTonE-Luc), it was demonstrated that a TonE site was sufficient for the hypertonicity-mediated activation of TauT promoter. Importantly, co-transfection of TauT promoter gene plasmid with wild-type TonEBP expression vector enhanced promoter activity under isotonic conditions, whereas dominant-negative TonEBP abrogated the TauT promoter activity induced by hypertonicity. Finally, treatment with taurine prevented HepG2 cells from cell death induced by hypertonic medium. These findings suggested that induction of TauT by hypertonicity is mediated by the activation of the TonE/TonEBP pathway and confers resistance to hypertonic stress.

Effect of high-NaCl or high-KCl diet on hepatic Na+- and K+-receptor sensitivity and NKCC1 expression in rats

We previously reported that the bumetanide-sensitive Na+-K+-2Cl-cotransporter (NKCC1) is involved in the hepatic Na+and K+sensor mechanism. In the present study, we examined the effects of a high-NaCl or high-KCl diet on hepatic Na+and K+receptor sensitivity and NKCC1 expression in the liver of Sprague-Dawley rats. RT-PCR and Western blots were used to measure NKCC1 mRNA and protein expression, respectively. Infusion of hypertonic NaCl or isotonic KCl + NaCl solutions into the portal vein increased hepatic afferent nerve activity (HANA) in a Na+or K+dose-dependent manner. After 4 wk on a high-NaCl or high-KCl diet, HANA responses were attenuated compared with animals fed a normal diet, and NKCC1 expression was reduced. These results show that a high-NaCl or high-KCl diet decreases NKCC1 expression in the liver, and it might cause a reduction in hepatic Na+- and K+-receptor sensitivity.

Call volume and insulin signaling

Perturbations of cell hydration as provoked by changes in ambient osmolarity or under isoosmotic conditions by hormones, second messengers, intracellular substrate accumulation, or reactive oxygen intermediates critically contribute to the physiological regulation of cell function. In general an increase in cell hydration stimulates anabolic metabolism and proliferation and provides cytoprotection, whereas cellular dehydration leads to a catabolic situation and sensitizes cells to apoptotic stimuli. Insulin produces cell swelling by inducing a net K+ and Na+ accumulation inside the cell, which results from a concerted activation of Na+/H+ exchange, Na+/K+/2Cl- symport, and the Na+/K(+)-ATPase. In the liver, insulin-induced cell swelling is critical for stimulation of glycogen and protein synthesis as well as inhibition of autophagic proteolysis. These insulin effects can largely be mimicked by hypoosmotic cell swelling, pointing to a role of cell swelling as a trigger of signal transduction. This article discusses insulin-induced signal transduction upstream of swelling and introduces the hypothesis that cell swelling as a signal amplifyer represents an essential component in insulin signaling, which contributes to the full response to insulin at the level of signal transduction and function. Cellular dehydration impairs insulin signaling and may be a major cause of insulin resistance, which develops in systemic hyperosmolarity, nutrient deprivation, uremia, oxidative challenges, and unbalanced production of insulin-counteracting hormones. Hydration changes affect cell functions at multiple levels (such as transcriptom, proteom, phosphoproteom, and the metabolom) and a system biological approach may allow us to develop a more holistic view on the hydration dependence of insulin signaling in the future.

Pharmacogenomics of diuretic drugs: data on rare monogenic disorders and on polymorphisms and requirements for further research

This review summarizes the current status of our knowledge about the role of pharmacogenetic variation in response to diuretics and suggests future research topics for the field. Genes with a role in the pharmacokinetics of most diuretics are renal drug transporters, especially OAT1, OAT3 and OCT2 (genes SLC22A6, SLC22A8 and SLC22A2) whereas variants in carbonic anhydrase (CA), cytochrome P450 enzymes and sulfotransferases are relevant only for specific substances. Genes on the pharmacodynamic side include the primary targets of thiazide, loop, K+-sparing and aldosterone antagonistic diuretics: NCC, NKCC2, ENaC and the mineralocorticoid receptor (genes SLC12A3, SLC12A1, SCNN1A, B, G and NR3C2). Rare variants of these proteins cause Gitelman’s syndrome, Bartter’s syndrome, Liddle’s syndrome or pregnancy-induced hypertension. Polymorphisms in these and in associated proteins such as GNB3, α-adducin and angiotensin-converting enzyme (ACE) seem to be clinically relevant. In conclusion, first knowledge has evolved that efficacy of diuretic drugs may be determined by genetic polymorphisms in genes determining pharmacokinetics and pharmacodynamics of this drug class. In the future, the selection of a diuretic drug or the dosing schedules may be individually chosen based on pharmacogenetic parameters, however, many questions remain to be answered before this fantasy becomes reality.