Neurogenic Mechanisms Contribute to Hypertension in Mice With Disruption of the K-Cl Cotransporter KCC3

Modus operandi of ClC-K2 Cl- Channel in the Collecting Duct Intercalated Cells

The renal collecting duct is known to play a critical role in many physiological processes, including systemic water-electrolyte homeostasis, acid-base balance, and the salt sensitivity of blood pressure. ClC-K2 (ClC-Kb in humans) is a Cl^--permeable channel expressed on the basolateral membrane of several segments of the renal tubule, including the collecting duct intercalated cells. ClC-Kb mutations are causative for Bartters' syndrome type 3 manifested as hypotension, urinary salt wasting, and metabolic alkalosis. However, little is known about the significance of the channel in the collecting duct with respect to the normal physiology and pathology of Bartters' syndrome. In this review, we summarize the available experimental evidence about the signaling determinants of ClC-K2 function and the regulation by systemic and local factors as well as critically discuss the recent advances in understanding the collecting-duct-specific roles of ClC-K2 in adaptations to changes in dietary Cl^- intake and maintaining systemic acid-base homeostasis.

KCC3a, a Strong Candidate Pathway for K+ Loss in Alkalemia

Loss-of-function mutations in the human potassium chloride cotransporter-3 (KCC3) cause a hereditary motor sensory neuropathy associated with agenesis of the corpus callosum. While recapitulating the neuropathy, KCC3-knockout mice also exhibit high blood pressure. This phenotype is believed to have neurogenic and/or vascular origins. The role of KCC3 in the kidney is poorly understood. KCC3 is encoded by two major isoforms originating from alternative promoters: KCC3a and KCC3b, with KCC3b being the predominant transcript in the kidney. Although the transporter has previously been localized to the proximal tubule, we show here the unique expression of the KCC3a isoform in the connecting tubule. Using a KCC3a-specific polyclonal antibody validated for both immunofluorescence and immunoblotting, we showed an intense KCC3a signal restricted to cortical intercalated cells. No overlap is detected between KCC3a and sodium chloride cotransporter (NCC), a distal convoluted tubule (DCT) marker; or between KCC3a and ENaC or calbindin, which are both principal cell markers. KCC3a signal was observed in cells expressing the apical V-ATPase and pendrin, establishing a unique expression pattern characteristic of intercalated cells of type-B or type-nonA/nonB. We further show that treatment of wild-type mice with hydrochlorothiazide, amiloride, or fed a K+-deficient diet up-regulates KCC3a level, suggesting that volume depletion increases KCC3a abundance. This hypothesis was confirmed by showing a higher abundance of KCC3a protein after 23-h water restriction or after placing the mice on a low-salt diet. More importantly, abundance of the Cl−/HCO3− exchanger, pendrin, which is known to secrete bicarbonate in alkalotic conditions, was significantly diminished in KCC3-knockout mice. In addition, KCC3a abundance increased significantly alongside pendrin abundance in bicarbonate-treated alkalotic mice, providing a credible mechanism for K+ loss in metabolic alkalosis.

Erythroid-specific inactivation of Slc12a6/Kcc3 by EpoR promoter-driven Cre expression reduces K-Cl cotransport activity in mouse erythrocytes

Investigation of erythrocytes from spontaneous or engineered germ‐line mutant mice has been instrumental in characterizing the physiological functions of components of the red cell cytoskeleton and membrane. However, the red blood cell expresses some proteins whose germline loss‐of‐function is embryonic‐lethal, perinatal‐lethal, or confers reduced post‐weaning viability.

Promoter regions of erythroid‐specific genes have been used to engineer erythroid‐specific expression of Cre recombinase. Through breeding with mice carrying appropriately spaced insertions of loxP sequences, generation of erythroid‐specific knockouts has been carried out for signaling enzymes, transcription factors, peptide hormones, and single transmembrane span signaling receptors. We report here the use of Cre recombinase expression driven by the erythropoietin receptor (EpoR) promoter to generate EpoR‐Cre;Kcc3^f/f mice, designed to express erythroid‐specific knockout of the KCC3 K‐Cl cotransporter encoded by Kcc3/Slc12A6. We confirm KCC3 as the predominant K‐Cl cotransporter of adult mouse red cells in mice with better viability than previously exhibited by Kcc3^−/− germline knockouts. We demonstrate roughly proportionate preservation of K‐Cl stimulation by hypotonicity, staurosporine, and urea in the context of reduced, but not abrogated, K‐Cl function in EpoR‐Cre;Kcc3^f/f mice. We also report functional evidence suggesting incomplete recombinase‐mediated excision of the Kcc3 gene in adult erythroid tissues.

The Important Role of Ion Transport System in Cervical Cancer

Cervical cancer is a significant gynecological cancer and causes cancer-related deaths worldwide. Human papillomavirus (HPV) is implicated in the etiology of cervical malignancy. However, much evidence indicates that HPV infection is a necessary but not sufficient cause in cervical carcinogenesis. Therefore, the cellular pathophysiology of cervical cancer is worthy of study. This review summarizes the recent findings concerning the ion transport processes involved in cell volume regulation and intracellular Ca²⁺ homeostasis of epithelial cells and how these transport systems are themselves regulated by the tumor microenvironment. For cell volume regulation, we focused on the volume-sensitive Cl⁻ channels and K⁺-Cl⁻ cotransporter (KCC) family, important regulators for ionic and osmotic homeostasis of epithelial cells. Regarding intracellular Ca²⁺ homeostasis, the Ca²⁺ store sensor STIM molecules and plasma membrane Ca²⁺ channel Orai proteins, the predominant Ca²⁺ entry mechanism in epithelial cells, are discussed. Furthermore, we evaluate the potential of these membrane ion transport systems as diagnostic biomarkers and pharmacological interventions and highlight the challenges.

Cation-coupled chloride cotransporters: chemical insights and disease implications

Cation-coupled chloride cotransporters (CCCs) modulate the transport of sodium and/or potassium cations coupled with chloride anions across the cell membrane. CCCs thus help regulate intracellular ionic concentration and consequent cell volume homeostasis. This has been largely exploited in the past to develop diuretic drugs that act on CCCs expressed in the kidney. However, a growing wealth of evidence has demonstrated that CCCs are also critically involved in a great variety of other pathologies, motivating most recent drug discovery programs targeting CCCs. Here, we examine the structure–function relationship of CCCs. By linking recent high-resolution cryogenic electron microscopy (cryo-EM) data with older biochemical/functional studies on CCCs, we discuss the mechanistic insights and opportunities to design selective CCC modulators to treat diverse pathologies.

The structural topology and function of all cation-coupled chloride cotransporters (CCCs) have been continuously investigated over the past 40 years, with great progress also thanks to the recent cryogenic electron microscopy (cryo-EM) resolution of the structures of five CCCs. In particular, such studies have clarified the structure–function relationship for the Na-K-Cl cotransporter NKCC1 and K-Cl cotransporters KCC1–4.

The constantly growing evidence of the crucial involvement of CCCs in physiological and various pathological conditions, as well as the evidence of their wide expression in diverse body tissues, has promoted CCCs as targets for the discovery and development of new, safer, and more selective/effective drugs for a plethora of pathologies.

Post-translational modification anchor points on the structure of CCCs may offer alternative strategies for small molecule drug discovery.

Increased intracellular Cl- concentration in pulmonary arterial myocytes is associated with chronic hypoxic pulmonary hypertension

Chloride channels play an important role in regulating smooth muscle contraction and proliferation, and contribute to the enhanced constriction of pulmonary arteries (PAs) in pulmonary hypertension (PH). The intracellular Cl^- concentration ([Cl^-]_i), tightly regulated by various Cl^- transporters, determines the driving force for Cl^- conductance, thereby the functional outcome of Cl^- channel activation. This study characterizes for the first time the expression profile of Cl^- transporters/exchangers in PA smooth muscle and provides the first evidence that the intracellular Cl^- homeostasis is altered in PA smooth muscle cells (PASMCs) associated with chronic hypoxic PH (CHPH). Quantitative RT-PCR revealed that the endothelium-denuded intralobar PA of rats expressed Slc12a gene family-encoded Na-K-2Cl cotransporter 1 (NKCC1), K-Cl cotransporters (KCC) 1, 3, and 4, and Slc4a gene family-encoded Na⁺-independent and Na⁺-dependent Cl^-/HCO₃^- exchangers. Exposure of rats to chronic hypoxia (10% O₂, 3 wk) caused CHPH and selectively increased the expression of Cl^--accumulating NKCC1 and reduced the Cl^--extruding KCC4. The intracellular Cl^- concentration ([Cl^-]_i) averaged at 45 mM and 47 mM in normoxic PASMCs as determined by fluorescent indicator MEQ and by gramicidin-perforated patch-clamp technique, respectively. The ([Cl^-]_i was increased by ∼10 mM in PASMCs of rats with CHPH. Future studies are warranted to further establish the hypothesis that the altered intracellular Cl^- homeostasis contributes to the pathogenesis of CHPH.

Anti-hyperprolactinemic activities of aqueous extract of Uvaria chamae (P. Beauv) roots and associated biochemical changes in chlorpromazine-induced hyperprolactinemic female Wistar rats

ETHNOPHARAMCOLOGICAL RELEVANCE

The age-long folkloric use of Uvaria chamae roots in the management of nipple discharge that is not related to pregnancy, childbirth or nursing but as a result of excessive production of prolactin (hyperprolactinemia) is yet to be substantiated with scientific data.

AIM OF THE STUDY

This study investigated the anti-hyperprolactinemic activities of aqueous extract of Uvaria chamae roots (AEUCR) and associated biochemical changes in chlorpromazine (CPZ)-induced hyperprolactinemic female Wistar rats.

MATERIALS AND METHODS

A total of sixty female rats (207.40 ± 2.69 g) were assigned into 6 groups: A-F. Animals in Group A received 0.5 ml of distilled water only whilst the 7 days CPZ-treated female rats (to induce hyperprolactinemia) in groups B, C, D, E, and F also received distilled water, 2.5 mg/kg body weight of bromocriptine (reference drug), 0.71, 1.41 2.83 mg/kg body weight of AEUCR for 28 days.

RESULTS

AEUCR contained a total of 15 (75%) amino acids with seven (46.67%) being essential amino acids and eight (53.33%) as non-essential amino acids. Administration of CPZ increased (p < 0.05) the levels of prolactin and testosterone, and reduced (p < 0.05) the levels of estradiol, progesterone, follicle stimulating hormone (FSH), luteinizing hormone (LH), dopamine, triiodothyronine (T3) and tetraiodothyroxine (T4). Chlorpromazine also increased the levels of serum urea, creatinine, total protein, albumin, globulin, bilirubin, alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) of the animals. In contrast, AEUCR significantly (p < 0.05) reduced the CPZ-induced increases in the levels of prolactin and testosterone, and increased the levels of CPZ-induced reduction in the progesterone, estradiol, FSH, LH, dopamine, T3 and T4. The AEUCR also reversed (p < 0.05) the CPZ-induced related increases in the levels of urea, creatinine, total protein, albumin, globulin, bilirubin, ALT, AST and ALP similar to the trends in the distilled water- and bromocriptine-treated controls. The CPZ-induced remarkable increase in the size of lactating alveolus and lactiferous duct distribution in the mammary gland were restored to normal tubule-alveolar female pattern mammary glands, composed of branching ducts and small alveoli budding off the ducts.

CONCLUSION

The study concluded that aqueous extract of Uvaria chamae root exhibited anti-hyperprolactinemic activity by restoring prolactin and dopamine levels and tubule-alveolar female pattern in female rats. It also ameliorated CPZ-induced changes in the liver and kidney function indices. This study justifies the folkloric use of Uvaria chamae root in the management of abnormal discharge by the nipples that is unrelated to pregnancy, childbirth and nursing.

Targeting the WNK-SPAK/OSR1 Pathway and Cation-Chloride Cotransporters for the Therapy of Stroke

Stroke is one of the major culprits responsible for morbidity and mortality worldwide, and the currently available pharmacological strategies to combat this global disease are scanty. Cation-chloride cotransporters (CCCs) are expressed in several tissues (including neurons) and extensively contribute to the maintenance of numerous physiological functions including chloride homeostasis. Previous studies have implicated two CCCs, the Na+-K+-Cl- and K+-Cl- cotransporters (NKCCs and KCCs) in stroke episodes along with their upstream regulators, the with-no-lysine kinase (WNKs) family and STE20/SPS1-related proline/alanine rich kinase (SPAK) or oxidative stress response kinase (OSR1) via a signaling pathway. As the WNK-SPAK/OSR1 pathway reciprocally regulates NKCC and KCC, a growing body of evidence implicates over-activation and altered expression of NKCC1 in stroke pathology whilst stimulation of KCC3 during and even after a stroke event is neuroprotective. Both inhibition of NKCC1 and activation of KCC3 exert neuroprotection through reduction in intracellular chloride levels and thus could be a novel therapeutic strategy. Hence, this review summarizes the current understanding of functional regulations of the CCCs implicated in stroke with particular focus on NKCC1, KCC3, and WNK-SPAK/OSR1 signaling and discusses the current and potential pharmacological treatments for stroke.

Role of the Cation-Chloride-Cotransporters in Cardiovascular Disease

The SLC12 family of cation-chloride-cotransporters (CCCs) is comprised of potassium chloride cotransporters (KCCs), which mediate Cl- extrusion and sodium-potassium chloride cotransporters (N[K]CCs), which mediate Cl- loading. The CCCs play vital roles in cell volume regulation and ion homeostasis. The functions of CCCs influence a variety of physiological processes, many of which overlap with the pathophysiology of cardiovascular disease. Although not all of the cotransporters have been linked to Mendelian genetic disorders, recent studies have provided new insights into their functional role in vascular and renal cells in addition to their contribution to cardiovascular diseases. Particularly, an imbalance in potassium levels promotes the pathogenesis of atherosclerosis and disturbances in sodium homeostasis are one of the causes of hypertension. Recent findings suggest hypothalamic signaling as a key signaling pathway in the pathophysiology of hypertension. In this review, we summarize and discuss the role of CCCs in cardiovascular disease with particular emphasis on knowledge gained in recent years on NKCCs and KCCs.

The WNK-SPAK/OSR1 Kinases and the Cation-Chloride Cotransporters as Therapeutic Targets for Neurological Diseases

In recent years, cation-chloride cotransporters (CCCs) have drawn attention in the medical neuroscience research. CCCs include the family of Na⁺-coupled Cl^- importers (NCC, NKCC1, and NKCC2), K⁺-coupled Cl^- exporters (KCCs), and possibly polyamine transporters (CCC9) and CCC interacting protein (CIP1). For decades, CCCs have been the targets of several commonly used diuretic drugs, including hydrochlorothiazide, furosemide, and bumetanide. Genetic mutations of NCC and NKCC2 cause congenital renal tubular disorders and lead to renal salt-losing hypotension, secondary hyperreninemia, and hypokalemic metabolic alkalosis. New studies reveal that CCCs along with their regulatory WNK (Kinase with no lysine (K)), and SPAK (Ste20-related proline-alanine-rich kinase)/OSR1(oxidative stress-responsive kinase-1) are essential for regulating cell volume and maintaining ionic homeostasis in the nervous system, especially roles of the WNK-SPAK-NKCC1 signaling pathway in ischemic brain injury and hypersecretion of cerebrospinal fluid in post-hemorrhagic hydrocephalus. In addition, disruption of Cl^- exporter KCC2 has an effect on synaptic inhibition, which may be involved in developing pain, epilepsy, and possibly some neuropsychiatric disorders. Interference with KCC3 leads to peripheral nervous system neuropathy as well as axon and nerve fiber swelling and psychosis. The WNK-SPAK/OSR1-CCCs complex emerges as therapeutic targets for multiple neurological diseases. This review will highlight these new findings.

Physiological roles and molecular mechanisms of K+ -Cl- cotransport in the mammalian kidney and cardiovascular system: where are we?

In the early 80s, renal microperfusion studies led to the identification of a basolateral K⁺ -Cl^- cotransport mechanism in the proximal tubule, thick ascending limb of Henle and collecting duct. More than ten years later, this mechanism was found to be accounted for by three different K⁺ -Cl^- cotransporters (KCC1, KCC3 and KCC4) that are differentially distributed along the renal epithelium. Two of these isoforms (KCC1 and KCC3) were also found to be expressed in arterial walls, the myocardium and a variety of neurons. Subsequently, valuable insights have been gained into the molecular and physiological properties of the KCCs in both the mammalian kidney and cardiovascular system. There is now robust evidence indicating that KCC4 sustains distal renal acidification and that KCC3 regulates myogenic tone in resistance vessels. However, progress in understanding the functional significance of these transporters has been slow, probably because each of the KCC isoforms is not identically distributed among species and some of them share common subcellular localizations with other KCC isoforms or sizeable conductive Cl^- pathways. In addition, the mechanisms underlying the process of K⁺ -Cl^- cotransport are still ill defined. The present review focuses on the knowledge gained regarding the roles and properties of KCCs in renal and cardiovascular tissues.

A role for KCC3 in maintaining cell volume of peripheral nerve fibers

The potassium chloride cotransporter, KCC3, is an electroneutral cotransporter expressed in the peripheral and central nervous system. KCC3 is responsible for the efflux of K+ and Cl- in neurons to help maintain cell volume and intracellular chloride levels. A loss-of-function (LOF) of KCC3 causes Hereditary Motor Sensory Neuropathy with Agenesis of the Corpus Callosum (HMSN/ACC) in a population of individuals in the Charlevoix/Lac-Saint-Jean region of Quebec, Canada. A variety of mouse models have been created to understand the physiological and deleterious effects of a KCC3 LOF. Though this KCC3 LOF in mouse models has recapitulated the peripheral neuropathy phenotype of HMSN/ACC, we still know little about the development of the disease pathophysiology. Interestingly, the most recent KCC3 mouse model that we created recapitulated a peripheral neuropathy-like phenotype originating from a KCC3 gain-of-function (GOF). Despite the past two decades of research in attempting to understand the role of KCC3 in disease, we still do not understand how dysfunction of this cotransporter can lead to the pathophysiology of peripheral neuropathy. This review focuses on the function of KCC3 in neurons and its role in human and health and disease.

Molecular insights into the normal operation, regulation, and multisystemic roles of K+-Cl- cotransporter 3 (KCC3)

Long before the molecular identity of the Na+-dependent K+-Cl- cotransporters was uncovered in the mid-nineties, a Na+-independent K+-Cl- cotransport system was also known to exist. It was initially observed in sheep and goat red blood cells where it was shown to be ouabain-insensitive and to increase in the presence of N-ethylmaleimide (NEM). After it was established between the early and mid-nineties, the expressed sequence tag (EST) databank was found to include a sequence that was highly homologous to those of the Na+-dependent K+-Cl- cotransporters. This sequence was eventually found to code for the Na+-independent K+-Cl- cotransport function that was described in red blood cells several years before. It was termed KCC1 and led to the discovery of three isoforms called KCC2, KCC3, and KCC4. Since then, it has become obvious that each one of these isoforms exhibits unique patterns of distribution and fulfills distinct physiological roles. Among them, KCC3 has been the subject of great attention in view of its important role in the nervous system and its association with a rare hereditary sensorimotor neuropathy (called Andermann syndrome) that affects many individuals in Quebec province (Canada). It was also found to play important roles in the cardiovascular system, the organ of Corti, and circulating blood cells. As will be seen in this review, however, there are still a number of uncertainties regarding the transport properties, structural organization, and regulation of KCC3. The same is true regarding the mechanisms by which KCC3 accomplishes its numerous functions in animal cells.

Molecular features and physiological roles of K+-Cl- cotransporter 4 (KCC4)

A K⁺-Cl^- cotransport system was documented for the first time during the mid-seventies in sheep and goat red blood cells. It was then described as a Na⁺-independent and ouabain-insensitive ion carrier that could be stimulated by cell swelling and N-ethylmaleimide (NEM), a thiol-reacting agent. Twenty years later, this system was found to be dispensed by four different isoforms in animal cells. The first one was identified in the expressed sequence tag (EST) database by Gillen et al. based on the assumption that it would be homologous to the Na⁺-dependent K⁺-Cl^- cotransport system for which the molecular identity had already been uncovered. Not long after, the three other isoforms were once again identified in the EST databank. Among those, KCC4 has generated much interest a few years ago when it was shown to sustain distal renal acidification and hearing development in mouse. As will be seen in this review, many additional roles were ascribed to this isoform, in keeping with its wide distribution in animal species. However, some of them have still not been confirmed through animal models of gene inactivation or overexpression. Along the same line, considerable knowledge has been acquired on the mechanisms by which KCC4 is regulated and the environmental cues to which it is sensitive. Yet, it is inferred to some extent from historical views and extrapolations.

With no lysine L-WNK1 isoforms are negative regulators of the K+-Cl- cotransporters

The K(+)-Cl(-) cotransporters (KCC1-KCC4) encompass a branch of the SLC12 family of electroneutral cation-coupled chloride cotransporters that translocate ions out of the cell to regulate various factors, including cell volume and intracellular chloride concentration, among others. L-WNK1 is an ubiquitously expressed kinase that is activated in response to osmotic stress and intracellular chloride depletion, and it is implicated in two distinct hereditary syndromes: the renal disease pseudohypoaldosteronism type II (PHAII) and the neurological disease hereditary sensory neuropathy 2 (HSN2). The effect of L-WNK1 on KCC activity is unknown. Using Xenopus laevis oocytes and HEK-293 cells, we show that the activation of KCCs by cell swelling was prevented by L-WNK1 coexpression. In contrast, the activity of the Na(+)-K(+)-2Cl(-) cotransporter NKCC1 was remarkably increased with L-WNK1 coexpression. The negative effect of L-WNK1 on the KCCs is kinase dependent. Elimination of the STE20 proline-alanine rich kinase (SPAK)/oxidative stress-responsive kinase (OSR1) binding site or the HQ motif required for the WNK-WNK interaction prevented the effect of L-WNK1 on KCCs, suggesting a required interaction between L-WNK1 molecules and SPAK. Together, our data support that NKCC1 and KCCs are coordinately regulated by L-WNK1 isoforms.

Ablation of Potassium-Chloride Cotransporter Type 3 (Kcc3) in Mouse Causes Multiple Cardiovascular Defects and Isosmotic Polyuria

Inactivation of Kcc3 in a mixed 129/Sv×C57BL/6 mouse background has been previously found to increase systemic blood pressure (BP) through presumed neurogenic mechanisms. Yet, while this background is generally not considered ideal to investigate the cardiovascular system, KCC3 is also expressed in the arterial wall and proximal nephron. In the current study, the effects of Kcc3 ablation was investigated in a pure rather than mixed C57BL/6J background under regular- and high-salt diets to determine whether they could be mediated through vasculogenic and nephrogenic mechanisms. Aortas were also assessed for reactivity to pharmacological agents while isolated from the influence of sympathetic ganglia. This approach led to the identification of unforeseen abnormalities such as lower pulse pressure, heart rate, aortic reactivity and aortic wall thickness, but higher diastolic BP, left ventricular mass and urinary output in the absence of increased catecholamine levels. Salt loading also led systolic BP to be higher, but to no further changes in hemodynamic parameters. Importantly, aortic vascular smooth muscle cells and cardiomyocytes were both found to express KCC3 abundantly in heterozygous mice. Hence, Kcc3 inactivation in our model caused systemic vascular resistance and ventricular mass to increase while preventing extracellular fluid volume to accumulate. Given that it also affected the physiological properties of aortas in vitro, vasculogenic mechanisms could therefore account for a number of the hemodynamic abnormalities observed.

Treatment effect of l-Norvaline on the sexual performance of male rats with streptozotocin induced diabetes

Sexual impairment is an established risk factor in diabetes mellitus affecting about 75% of male diabetic population. In diabetes overexpression of arginase leads to decreased production of NO and diminished erectile response. Inhibition of arginase enzyme can lead to improvement in diabetes induced sexual dysfunction. In the present study diabetes mellitus was induced in adult male rats by intraperitoneal injection of single dose of streptozotocin (65mg/kg) in 0.1M Citrate buffer pH 4.5 and after 72h fasting serum glucose level was checked by glucose oxidase-peroxidase method and those animals showing FSG above 250mg/dl were selected. Diabetic animals were divided into four groups comprising six animals in each. l-Norvaline, potent arginase inhibitor was administered at a dose of 10mg/kg ip to the different groups of diabetic animals for a period of 30 days. Sildenafil at a dose of 5mg/kg orally was used as a standard drug. Mating behavior tests were performed at 0, 15th and 30th days. After 30 days, various biochemical and hormonal parameters (nitrates, LDH, urea, testosterone), testicular parameters (total protein, nitrates, LDH, total cholesterol, LDL, triglycerides, VLDL, HDL) were evaluated to find out the effect of l-Norvaline in sexual impairment. Sperm analysis was also carried out for the treated rats. l-Norvaline showed significant improvement in serum nitrates, urea, LDH, testosterone and testicular protein level as compared with diabetic group. It also improved sperm motility, count and viability in diabetic rats. Sildenafil showed no improvement in above parameters except restoration in serum nitrates level.

In Vivo Evidence for Lysosome Depletion and Impaired Autophagic Clearance in Hereditary Spastic Paraplegia Type SPG11

Hereditary spastic paraplegia (HSP) is characterized by a dying back degeneration of corticospinal axons which leads to progressive weakness and spasticity of the legs. SPG11 is the most common autosomal-recessive form of HSPs and is caused by mutations in SPG11. A recent in vitro study suggested that Spatacsin, the respective gene product, is needed for the recycling of lysosomes from autolysosomes, a process known as autophagic lysosome reformation. The relevance of this observation for hereditary spastic paraplegia, however, has remained unclear. Here, we report that disruption of Spatacsin in mice indeed causes hereditary spastic paraplegia-like phenotypes with loss of cortical neurons and Purkinje cells. Degenerating neurons accumulate autofluorescent material, which stains for the lysosomal protein Lamp1 and for p62, a marker of substrate destined to be degraded by autophagy, and hence appears to be related to autolysosomes. Supporting a more generalized defect of autophagy, levels of lipidated LC3 are increased in Spatacsin knockout mouse embryonic fibrobasts (MEFs). Though distinct parameters of lysosomal function like processing of cathepsin D and lysosomal pH are preserved, lysosome numbers are reduced in knockout MEFs and the recovery of lysosomes during sustained starvation impaired consistent with a defect of autophagic lysosome reformation. Because lysosomes are reduced in cortical neurons and Purkinje cells in vivo, we propose that the decreased number of lysosomes available for fusion with autophagosomes impairs autolysosomal clearance, results in the accumulation of undegraded material and finally causes death of particularly sensitive neurons like cortical motoneurons and Purkinje cells in knockout mice.

Autophagy is a degradative pathway for the removal and subsequent recycling of dysfunctional intracellular components. The material destined for degradation is initially enclosed by a double membrane, the autophagosome. In autolysosomes, which result from fusion of autophagosomes with lysosomes, the material is finally broken down. Recent in vitro data suggested that the protein Spatacsin plays a pivotal role in the regeneration of lysosomes from autolysosomes. Spatacsin is encoded by SPG11, the most common gene mutated in autosomal recessive hereditary spastic paraplegia. Here we show that mice devoid of Spatacsin develop symptoms consistent with spastic paraplegia and progressively loose cortical motoneurons and Purkinje cells. In these mice degenerating neurons have a reduced number of lysosomes available for fusion with autophagosomes and consequently accumulate autolysosome-derived material over time. In the long term this causes death of particularly sensitive neurons like cortical motoneurons and Purkinje cells.

Disruption of vascular Ca2+-activated chloride currents lowers blood pressure

High blood pressure is the leading risk factor for death worldwide. One of the hallmarks is a rise of peripheral vascular resistance, which largely depends on arteriole tone. Ca2+-activated chloride currents (CaCCs) in vascular smooth muscle cells (VSMCs) are candidates for increasing vascular contractility. We analyzed the vascular tree and identified substantial CaCCs in VSMCs of the aorta and carotid arteries. CaCCs were small or absent in VSMCs of medium-sized vessels such as mesenteric arteries and larger retinal arterioles. In small vessels of the retina, brain, and skeletal muscle, where contractile intermediate cells or pericytes gradually replace VSMCs, CaCCs were particularly large. Targeted disruption of the calcium-activated chloride channel TMEM16A, also known as ANO1, in VSMCs, intermediate cells, and pericytes eliminated CaCCs in all vessels studied. Mice lacking vascular TMEM16A had lower systemic blood pressure and a decreased hypertensive response following vasoconstrictor treatment. There was no difference in contractility of medium-sized mesenteric arteries; however, responsiveness of the aorta and small retinal arterioles to the vasoconstriction-inducing drug U46619 was reduced. TMEM16A also was required for peripheral blood vessel contractility, as the response to U46619 was attenuated in isolated perfused hind limbs from mutant mice. Out data suggest that TMEM16A plays a general role in arteriolar and capillary blood flow and is a promising target for the treatment of hypertension.

A hereditary spastic paraplegia mouse model supports a role of ZFYVE26/SPASTIZIN for the endolysosomal system

Hereditary spastic paraplegias (HSPs) are characterized by progressive weakness and spasticity of the legs because of the degeneration of cortical motoneuron axons. SPG15 is a recessively inherited HSP variant caused by mutations in the ZFYVE26 gene and is additionally characterized by cerebellar ataxia, mental decline, and progressive thinning of the corpus callosum. ZFYVE26 encodes the FYVE domain-containing protein ZFYVE26/SPASTIZIN, which has been suggested to be associated with the newly discovered adaptor protein 5 (AP5) complex. We show that Zfyve26 is broadly expressed in neurons, associates with intracellular vesicles immunopositive for the early endosomal marker EEA1, and co-fractionates with a component of the AP5 complex. As the function of ZFYVE26 in neurons was largely unknown, we disrupted Zfyve26 in mice. Zfyve26 knockout mice do not show developmental defects but develop late-onset spastic paraplegia with cerebellar ataxia confirming that SPG15 is caused by ZFYVE26 deficiency. The morphological analysis reveals axon degeneration and progressive loss of both cortical motoneurons and Purkinje cells in the cerebellum. Importantly, neuron loss is preceded by accumulation of large intraneuronal deposits of membrane-surrounded material, which co-stains with the lysosomal marker Lamp1. A density gradient analysis of brain lysates shows an increase of Lamp1-positive membrane compartments with higher densities in Zfyve26 knockout mice. Increased levels of lysosomal enzymes in brains of aged knockout mice further support an alteration of the lysosomal compartment upon disruption of Zfyve26. We propose that SPG15 is caused by an endolysosomal membrane trafficking defect, which results in endolysosomal dysfunction. This appears to be particularly relevant in neurons with highly specialized neurites such as cortical motoneurons and Purkinje cells.

Hereditary spastic paraplegias (HSPs) are inherited disorders characterized by progressive weakness and spasticity of the legs. In HSP patients, nerve fibers connecting cortical motoneurons with spinal cord neurons are progressively lost. HSP subtype 15 (SPG15) is caused by mutations in ZFYVE26, and is characterized by additional cerebellar symptoms. We show that the Zfyve26 protein is broadly expressed in the brain. At the subcellular level Zfyve26 localizes to an intracellular compartment in the endocytic pathway from the plasma membrane to lysosomes, which is part of the degradative system of the cell. Closely resembling the human disease, mice deficient for Zfyve26 develop a progressive spastic gait disorder with cerebellar symptoms and degeneration of both neurons of the motor cortex and Purkinje cells in the cerebellum. Importantly, this degeneration is characterized by the intracellular accumulation of abnormal deposits, which stain positive for the lysosomal marker Lamp1. As Zfyve26 has been shown to interact with the newly identified adaptor complex AP5, which is supposed to be involved in cargo trafficking in the endolysosomal compartment, endolysosomal dysfunction may be caused by a targeting defect upon disruption of Zfyve26. As highly specialized neurons like cortical motoneurons and cerebellar Purkinje cells degenerate, these neurons appear to be particularly dependent on proper endolysosomal function.

Mutations in GMPPA cause a glycosylation disorder characterized by intellectual disability and autonomic dysfunction

In guanosine diphosphate (GDP)-mannose pyrophosphorylase A (GMPPA), we identified a homozygous nonsense mutation that segregated with achalasia and alacrima, delayed developmental milestones, and gait abnormalities in a consanguineous Pakistani pedigree. Mutations in GMPPA were subsequently found in ten additional individuals from eight independent families affected by the combination of achalasia, alacrima, and neurological deficits. This autosomal-recessive disorder shows many similarities with triple A syndrome, which is characterized by achalasia, alacrima, and variable neurological deficits in combination with adrenal insufficiency. GMPPA is a largely uncharacterized homolog of GMPPB. GMPPB catalyzes the formation of GDP-mannose, which is an essential precursor of glycan moieties of glycoproteins and glycolipids and is associated with congenital and limb-girdle muscular dystrophies with hypoglycosylation of α-dystroglycan. Surprisingly, GDP-mannose pyrophosphorylase activity was unchanged and GDP-mannose levels were strongly increased in lymphoblasts of individuals with GMPPA mutations. This suggests that GMPPA might serve as a GMPPB regulatory subunit mediating feedback inhibition of GMPPB instead of displaying catalytic enzyme activity itself. Thus, a triple-A-like syndrome can be added to the growing list of congenital disorders of glycosylation, in which dysregulation rather than mere enzyme deficiency is the basal pathophysiological mechanism.

Molecular evidence for a role for K(+)-Cl(-) cotransporters in the kidney

K(+)-Cl(-) cotransporter (KCC) isoforms 3 (KCC3) and 4 (KCC4) are expressed at the basolateral membrane of proximal convoluted tubule cells, and KCC4 is present in the basolateral membrane of the thick ascending loop of Henle's limb and α-intercalated cells of the collecting duct. Little is known, however, about the physiological roles of these transporters in the kidney. We evaluated KCC3 and KCC4 mRNA and protein expression levels and intrarenal distribution in male Wistar rats or C57 mice under five experimental conditions: hyperglycemia after a single dose of streptozotocin, a low-salt diet, metabolic acidosis induced by ammonium chloride in drinking water, and low- or high-K(+) diets. Both KCC3 mRNA and protein expression were increased during hyperglycemia in the renal cortex and at the basolateral membrane of proximal tubule cells but not with a low-salt diet or acidosis. In contrast, KCC4 protein expression was increased by a low-sodium diet in the whole kidney and by metabolic acidosis in the renal outer medulla, specifically at the basolateral membrane of α-intercalated cells. The increased protein expression of KCC4 by a low-salt diet was also observed in WNK4 knockout mice, suggesting that upregulation of KCC4 in these circumstances is not WNK4 dependent. No change in KCC3 or KCC4 protein expression was observed under low- or high-K(+) diets. Our data are consistent with a role for KCC3 in the proximal tubule glucose reabsorption mechanism and for KCC4 in salt reabsorption of the thick ascending loop of Henle's loop and acid secretion of the collecting duct.

N-terminal serine dephosphorylation is required for KCC3 cotransporter full activation by cell swelling

The K⁺:Cl⁻ cotransporter (KCC) activity is modulated by phosphorylation/dephosphorylation processes. In isotonic conditions, KCCs are inactive and phosphorylated, whereas hypotonicity promotes their dephosphorylation and activation. Two phosphorylation sites (Thr-991 and Thr-1048) in KCC3 have been found to be critical for its regulation. However, here we show that the double mutant KCC3-T991A/T1048A could be further activated by hypotonicity, suggesting that additional phosphorylation site(s) are involved. We observed that in vitro activated STE20/SPS1-related proline/alanine-rich kinase (SPAK) complexed to its regulatory MO25 subunit phosphorylated KCC3 at Ser-96 and that in Xenopus laevis oocytes Ser-96 of human KCC3 is phosphorylated in isotonic conditions and becomes dephosphorylated during incubation in hypotonicity, leading to a dramatic increase in KCC3 function. Additionally, WNK3, which inhibits the activity of KCC3, promoted phosphorylation of Ser-96 as well as Thr-991 and Thr-1048. These observations were corroborated in HEK293 cells stably transfected with WNK3. Mutation of Ser-96 alone (KCC3-S96A) had no effect on the activity of the cotransporter when compared with wild type KCC3. However, when compared with the double mutant KCC3-T991A/T1048A, the triple mutant KCC3-S96A/T991A/T1048A activity in isotonic conditions was significantly higher, and it was not further increased by hypotonicity or inhibited by WNK3. We conclude that serine residue 96 of human KCC3 is a third site that has to be dephosphorylated for full activation of the cotransporter during hypotonicity.

A trafficking-deficient mutant of KCC3 reveals dominant-negative effects on K-Cl cotransport function

The K-Cl cotransporter (KCC) functions in maintaining chloride and volume homeostasis in a variety of cells. In the process of cloning the mouse KCC3 cDNA, we came across a cloning mutation (E289G) that rendered the cotransporter inactive in functional assays in Xenopus laevis oocytes. Through biochemical studies, we demonstrate that the mutant E289G cotransporter is glycosylation-deficient, does not move beyond the endoplasmic reticulum or the early Golgi, and thus fails to reach the plasma membrane. We establish through co-immunoprecipitation experiments that both wild-type and mutant KCC3 with KCC2 results in the formation of hetero-dimers. We further demonstrate that formation of these hetero-dimers prevents the proper trafficking of the cotransporter to the plasma membrane, resulting in a significant decrease in cotransporter function. This effect is due to interaction between the K-Cl cotransporter isoforms, as this was not observed when KCC3-E289G was co-expressed with NKCC1. Our studies also reveal that the glutamic acid residue is essential to K-Cl cotransporter function, as the corresponding mutation in KCC2 also leads to an absence of function. Interestingly, mutation of this conserved glutamic acid residue in the Na(+)-dependent cation-chloride cotransporters had no effect on NKCC1 function in isosmotic conditions, but diminished cotransporter activity under hypertonicity. Together, our data show that the glutamic acid residue (E289) is essential for proper trafficking and function of KCCs and that expression of a non-functional but full-length K-Cl cotransporter might results in dominant-negative effects on other K-Cl cotransporters.

The SLC12 family of electroneutral cation-coupled chloride cotransporters

The SLC12 family encodes electroneutral cation-coupled chloride cotransporters that are critical for several physiological processes including cell volume regulation, modulation of intraneuronal chloride concentration, transepithelial ion movement, and blood pressure regulation. Members of this family are the targets of the most commonly used diuretic drugs, have been shown to be the causative genes for inherited disease such as Gitelman, Bartter and Andermann syndromes, and potentially play a role in polygenic complex diseases like arterial hypertension, epilepsy, osteoporosis, and cancer.

Physiology of SLC12 transporters: lessons from inherited human genetic mutations and genetically engineered mouse knockouts

Among the over 300 members of the solute carrier (SLC) group of integral plasma membrane transport proteins are the nine electroneutral cation-chloride cotransporters belonging to the SLC12 gene family. Seven of these transporters have been functionally described as coupling the electrically silent movement of chloride with sodium and/or potassium. Although in silico analysis has identified two additional SLC12 family members, no physiological role has been ascribed to the proteins encoded by either the SLC12A8 or the SLC12A9 genes. Evolutionary conservation of this gene family from protists to humans confirms their importance. A wealth of physiological, immunohistochemical, and biochemical studies have revealed a great deal of information regarding the importance of this gene family to human health and disease. The sequencing of the human genome has provided investigators with the capability to link several human diseases with mutations in the genes encoding these plasma membrane proteins. The availability of bacterial artificial chromosomes, recombination engineering techniques, and the mouse genome sequence has simplified the creation of targeting constructs to manipulate the expression/function of these cation-chloride cotransporters in the mouse in an attempt to recapitulate some of these human pathologies. This review will summarize the three human disorders that have been linked to the mutation/dysfunction of the Na-Cl, Na-K-2Cl, and K-Cl cotransporters (i.e., Bartter's, Gitleman's, and Andermann's syndromes), examine some additional pathologies arising from genetically modified mouse models of these cotransporters including deafness, blood pressure, hyperexcitability, and epithelial transport deficit phenotypes.

Raising cytosolic Cl- in cerebellar granule cells affects their excitability and vestibulo-ocular learning

Cerebellar cortical throughput involved in motor control comprises granule cells (GCs) and Purkinje cells (PCs), both of which receive inhibitory GABAergic input from interneurons. The GABAergic input to PCs is essential for learning and consolidation of the vestibulo-ocular reflex, but the role of GC excitability remains unclear. We now disrupted the Kcc2 K-Cl cotransporter specifically in either cell type to manipulate their excitability and inhibition by GABA(A)-receptor Cl(-) channels. Although Kcc2 may have a morphogenic role in synapse development, Kcc2 disruption neither changed synapse density nor spine morphology. In both GCs and PCs, disruption of Kcc2, but not Kcc3, increased [Cl(-)](i) roughly two-fold. The reduced Cl(-) gradient nearly abolished GABA-induced hyperpolarization in PCs, but in GCs it merely affected excitability by membrane depolarization. Ablation of Kcc2 from GCs impaired consolidation of long-term phase learning of the vestibulo-ocular reflex, whereas baseline performance, short-term gain-decrease learning and gain consolidation remained intact. These functions, however, were affected by disruption of Kcc2 in PCs. GC excitability plays a previously unknown, but specific role in consolidation of phase learning.

Cation-chloride cotransporters and neuronal function

Recent years have witnessed a steep increase in studies on the diverse roles of neuronal cation-chloride cotransporters (CCCs). The versatility of CCC gene transcription, posttranslational modification, and trafficking are on par with what is known about ion channels. The cell-specific and subcellular expression patterns of different CCC isoforms have a key role in modifying a neuron's electrophysiological phenotype during development, synaptic plasticity, and disease. While having a major role in controlling responses mediated by GABA(A) and glycine receptors, CCCs also show close interactions with glutamatergic signaling. A cross-talk among CCCs and trophic factors is important in short-term and long-term modification of neuronal properties. CCCs appear to be multifunctional proteins that are also involved in shaping neuronal structure at various stages of development, from stem cells to synaptogenesis. The rapidly expanding work on CCCs promotes our understanding of fundamental mechanisms that control brain development and functions under normal and pathophysiological conditions.

Other Transgenic Animal Models Used in Cardiovascular Studies

Previous chapters have described a large number of transgenic animal models used to study specific cardiovascular syndromes. This chapter will fill in some gaps. Many of these transgenic animals were developed to study normal and/or abnormal physiological responses in other organ systems, or to study basic biochemical and molecular reactions or pathways. These models were then discovered to also have effects on the cardiovascular system, some of them unanticipated.

A word of caution, particularly when highly inbred mouse strains are used to develop transgenic models - not all strains of a particular species are created equal. When cardiovascular parameters of age- and sex-matched A/J and C57BL/6J inbred mice were compared the C57BL/6J mice demonstrated eccentric physiologic ventricular hypertrophy, increased ventricular function, lower heart rates, and increased exercise endurance.¹

Functional analysis of a potassium-chloride co-transporter 3 (SLC12A6) promoter polymorphism leading to an additional DNA methylation site

The human potassium-chloride co-transporter 3 (KCC3, SLC12A6) is involved in cell proliferation and in electro-neutral movement of ions across the cell membrane. The gene (SLC12A6) is located on chromosome 15q14, a region that has previously shown linkage with bipolar disorder, schizophrenia, rolandic epilepsy, idiopathic generalized epilepsy, autism and attention deficit/hyperactivity disorder. Furthermore, recessively inherited mutations of SLC12A6 cause Andermann syndrome, characterized by agenesis of the corpus callosum, which is associated with peripheral neuropathy and psychoses. Recently, we have demonstrated the association of two G/A promoter polymorphisms of SLC12A6 with bipolar disorder in a case-control study, and familial segregation of the rare variants as well as a trend toward association with schizophrenia. To investigate functional consequences of these polymorphisms, lymphocyte DNA was extracted, bisulfite modified, and subsequently sequenced. To investigate SLC12A6 promoter activity, various promoter constructs were generated and analyzed by luciferase reporter gene assays. We provide evidence that the G- allele showed a significant reduction of reporter gene expression. In human lymphocytes, the allele harboring the rare upstream G nucleotide was found to be methylated at the adjacent C position, possibly accountable for tissue-specific reduction in gene expression in vivo. Here we demonstrate functionality of an SNP associated with psychiatric disease and our results may represent a functional link between genetic variation and an epigenetic modification.

Sodium-, potassium-, chloride-, and bicarbonate-related effects on blood pressure and electrolyte homeostasis in deoxycorticosterone acetate-treated rats

Na(+) loading without Cl(-) fails to increase blood pressure in the DOCA model. We compared the changes in the total body (TB) effective Na(+), K(+), Cl(-), and water (TBW) content as well as in intracellular (ICV) or extracellular (ECV) volume in rats receiving DOCA-NaCl, DOCA-NaHCO(3), or DOCA-KHCO(3). We divided 42 male rats into 5 groups. Group 1 was untreated, group 2 received 1% NaCl, and groups 3, 4, and 5 were treated with DOCA and received 1% NaCl, 1.44% NaHCO(3), or 1.7% KHCO(3) to drink. We measured mean arterial blood pressure (MAP) directly after 3 wk. Tissue electrolyte and water content was measured by chemical analysis. Compared with control rats, DOCA-NaCl increased MAP while DOCA-NaHCO(3) and DOCA-KHCO(3) did not. DOCA-NaCl increased TBNa(+) 26% but only moderately increased TBW. DOCA-NaHCO(3) led to similar TBNa(+) excess, while TBW and ICV, but not ECV, were increased more than in DOCA-NaCl rats. DOCA-KHCO(3) did not affect TBNa(+) or volume. At a given TB(Na(+)+K(+)) and TBW, MAP in DOCA-NaCl rats was higher than in control, DOCA-NaHCO(3), and DOCA-KHCO(3) rats, indicating that hypertension in DOCA-NaCl rats was not dependent on TB(Na(+)+K(+)) and water mass balance. Skin volume retention was hypertonic compared with serum and paralleled hypertension in DOCA-NaCl rats. These rats had higher TB(Na(+)+K(+))-to-TBW ratio in accumulated fluid than DOCA-NaHCO(3) rats. DOCA-NaCl rats also had increased intracellular Cl(-) concentrations in skeletal muscle. We conclude that excessive cellular electrolyte redistribution and/or intracellular Na(+) or Cl(-) accumulation may play an important role in the pathogenesis of salt-sensitive hypertension.

Disruption of erythroid K-Cl cotransporters alters erythrocyte volume and partially rescues erythrocyte dehydration in SAD mice

K-Cl cotransport activity in rbc is a major determinant of rbc volume and density. Pathologic activation of erythroid K-Cl cotransport activity in sickle cell disease contributes to rbc dehydration and cell sickling. To address the roles of individual K-Cl cotransporter isoforms in rbc volume homeostasis, we disrupted the Kcc1 and Kcc3 genes in mice. As rbc K-Cl cotransport activity was undiminished in Kcc1(-/-) mice, decreased in Kcc3(-/-) mice, and almost completely abolished in mice lacking both isoforms, we conclude that K-Cl cotransport activity of mouse rbc is mediated largely by KCC3. Whereas rbc of either Kcc1(-/-) or Kcc3(-/-) mice were of normal density, rbc of Kcc1(-/-)Kcc3(-/-) mice exhibited defective volume regulation, including increased mean corpuscular volume, decreased density, and increased susceptibility to osmotic lysis. K-Cl cotransport activity was increased in rbc of SAD mice, which are transgenic for a hypersickling human hemoglobin S variant. Kcc1(-/-)Kcc3(-/-) SAD rbc lacked nearly all K-Cl cotransport activity and exhibited normalized values of mean corpuscular volume, corpuscular hemoglobin concentration mean, and K(+) content. Although disruption of K-Cl cotransport rescued the dehydration phenotype of most SAD rbc, the proportion of the densest red blood cell population remained unaffected.

WNK4 kinase is a negative regulator of K+-Cl- cotransporters

WNK kinases [with no lysine (K) kinase] are emerging as regulators of several membrane transport proteins in which WNKs act as molecular switches that coordinate the activity of several players. Members of the cation-coupled chloride cotransporters family (solute carrier family number 12) are one of the main targets. WNK3 activates the Na(+)-driven cotransporters NCC, NKCC1, and NKCC2 and inhibits the K(+)-driven cotransporters KCC1 to KCC4. WNK4 inhibits the activity of NCC and NKCC1, while in the presence of the STE20-related proline-alanine-rich kinase SPAK activates NKCC1. Nothing is known, however, regarding the effect of WNK4 on the K(+)-Cl(-) cotransporters. Using the heterologous expression system of Xenopus laevis oocytes, here we show that WNK4 inhibits the activity of the K(+)-Cl(-) cotransporters KCC1, KCC3, and KCC4 under cell swelling, a condition in which these cotransporters are maximally active. The effect of WNK4 requires its catalytic activity because it was lost by the substitution of aspartate 318 for alanine (WNK4-D318A) that renders WNK4 catalytically inactive. In contrast, three different WNK4 missense mutations that cause pseudohypoaldosteronism type II do not affect the WNK4-induced inhibition of KCC4. Finally, we observed that catalytically inactive WNK4-D318A is able to bypass the tonicity requirements for KCC2 and KCC3 activation in isotonic conditions. This effect is enhanced by the presence of catalytically inactive SPAK, was prevented by the presence of protein phosphatase inhibitors, and was not present in KCC1 and KCC4. Our results reveal that WNK4 regulates the activity of the K(+)-Cl(-) cotransporters expressed in the kidney.

WNK protein kinases modulate cellular Cl- flux by altering the phosphorylation state of the Na-K-Cl and K-Cl cotransporters

Precise control of cellular Cl(-) transport is necessary for many fundamental physiological processes. For example, the intracellular concentration of Cl(-), fine-tuned through the coordinated action of cellular Cl(-) influx and efflux mechanisms, determines whether a neuron's response to GABA is excitatory or inhibitory. In epithelia, synchrony between apical and basolateral Cl(-) flux, and transcellular and paracellular Cl(-) transport, is necessary for efficient transepithelial Cl(-) reabsorption or secretion. In cells throughout the body, coordination of Cl(-) entry and exit mechanisms help defend against changes in cell volume. The Na-K-Cl and K-Cl cotransporters of the SLC12 gene family are important molecular determinants of Cl(-) entry and exit, respectively, in these systems. The WNK serine-threonine kinase family, members of which are mutated in an inherited form of human hypertension, are components of a signaling pathway that coordinates Cl(-) influx and efflux through SLC12 cotransporters to dynamically regulate intracellular Cl(-) activity.