Hypotonicity-Induced Renin Exocytosis from Juxtaglomerular Cells Requires Aquaporin-1 and Cyclooxygenase-2

The mechanism by which extracellular hypotonicity stimulates release of renin from juxtaglomerular (JG) cells is unknown. We hypothesized that osmotically induced renin release depends on water movement through aquaporin-1 (AQP1) water channels and subsequent prostanoid formation. We recorded membrane capacitance (C_m) by whole-cell patch clamp in single JG cells as an index of exocytosis. Hypotonicity increased C_m significantly and enhanced outward current. Indomethacin, PLA₂ inhibition, and an antagonist of prostaglandin transport impaired the C_m and current responses to hypotonicity. Hypotonicity also increased exocytosis as determined by a decrease in single JG cell quinacrine fluorescence in an indomethacin-sensitive manner. In single JG cells from COX-2^{−/ −} and AQP1^{−/ −} mice, hypotonicity increased neither C_m nor outward current, but 0.1-μM PGE₂ increased both in these cells. A reduction in osmolality enhanced cAMP accumulation in JG cells but not in renin-producing As4.1 cells; only the former had detectable AQP1 expression. Inhibition of protein kinase A blocked the hypotonicity-induced C_m and current response in JG cells. Taken together, our results show that a 5 to 7% decrease in extracellular tonicity leads to AQP1-mediated water influx in JG cells, PLA₂/COX-2-mediated prostaglandin-dependent formation of cAMP, and activation of PKA, which promotes exocytosis of renin.Juxtaglomerular (JG) granular cells in the terminal part of the renal afferent glomerular arterioles are the only cells in the organism that synthesize preprorenin, process it to active renin, and store active renin in mature secretory granules. The rate of renin granule exocytosis determines the level of activation of the renin-angiotensin-aldosterone system. Renin secretion from most^1,2 but not all^3,4 in vitro preparations displays a uniquely high sensitivity to changes in extracellular osmolality such that a moderate reduction in the extracellular osmolality leads to rapid increases in renin secretion. The sensing and transduction events for renin release in response to osmotic perturbations are not known. At the glomerular tuft, the extracellular osmolality may vary depending on sodium chloride (NaCl)transport rate by the adjacent macula densa and thick ascending limb cells, which are relatively water impermeable.^5,6 JG cell capacitance (C_m), an index of cell surface area, increased when extracellular osmolality was decreased by 5 to 10% at the single cell level.⁷ This observation shows exocytotic release of renin in response to decreases in extracellular osmolality.⁷ Introduction of a pipette solution with slightly increased osmolality to the cell cytoplasm is sufficient to initiate exocytosis of renin in JG cells.⁷ This indicates that cell swelling, and not granule swelling, is involved in the response and shows that sensing and transduction of the initial change in osmolality is not dependent on an extracellular receptor for the agent used (e.g., sucrose or mannitol), as shown recently to be the case for succinate.⁴ The estimated number of granules recruited for exocytosis by a hypotonic extracellular challenge corresponded closely to the number that fused after receptor-dependent activation of cAMP formation.⁷ The existing data predict an involvement of water fluxes across the JG cell membrane, but aquaporin water channels have not been demonstrated in JG cells. Marked cell swelling normally initiates a regulatory volume decrease response whereby the cell, through coordinated activation of ion and organic osmolyte efflux, regains cell volume.⁸ A distinct role for phospholipase A2 (PLA₂) and prostaglandin E2(PGE₂) EP2 receptors in swelling-induced activation of regulatory processes in single cells has been demonstrated.⁹ Prostaglandin E₂ and PGI₂ enhance outward current and renin secretion from JG cells.¹⁰ In the study presented here, we hypothesized that JG cells respond to a decrease in extracellular osmolality by water uptake, Cyclooxygenase (COX)-dependent prostaglandin formation and renin release. The hypotheses were tested using single JG cells subjected to whole-cell patch-clamp analysis and primary cultures enriched in JG cells from rats, wild-type mice, and mice with targeted deletions of COX-2 and aquaporin-1 (AQP1).     

Plasmin in Nephrotic Urine Activates the Epithelial Sodium Channel

Proteinuria and increased renal reabsorption of NaCl characterize the nephrotic syndrome. Here, we show that protein-rich urine from nephrotic rats and from patients with nephrotic syndrome activate the epithelial sodium channel (ENaC) in cultured M-1 mouse collecting duct cells and in Xenopus laevis oocytes heterologously expressing ENaC. The activation depended on urinary serine protease activity. We identified plasmin as a urinary serine protease by matrix-assisted laser desorption/ionization time of-flight mass spectrometry. Purified plasmin activated ENaC currents, and inhibitors of plasmin abolished urinary protease activity and the ability to activate ENaC. In nephrotic syndrome, tubular urokinase-type plasminogen activator likely converts filtered plasminogen to plasmin. Consistent with this, the combined application of urokinase-type plasminogen activator and plasminogen stimulated amiloride-sensitive transepithelial sodium transport in M-1 cells and increased amiloride-sensitive whole-cell currents in Xenopus laevis oocytes heterologously expressing ENaC. Activation of ENaC by plasmin involved cleavage and release of an inhibitory peptide from the ENaC γ subunit ectodomain. These data suggest that a defective glomerular filtration barrier allows passage of proteolytic enzymes that have the ability to activate ENaC.Nephrotic syndrome is characterized by proteinuria, sodium retention, and edema. Increased renal sodium reabsorption occurs in the cortical collecting duct (CCD),^1,2 where a rate-limiting step in transepithelial sodium transport is the epithelial sodium channel (ENaC), which is composed of the three homologous subunits: α, β, γ.³ENaC activity is regulated by hormones, such as aldosterone and vasopressin (AVP)^4,5; however, adrenalectomized rats and AVP-deficient Brattleboro rats are capable of developing nephrotic syndrome,^1,6 and nephrotic patients do not consistently display elevated levels of sodium-retaining hormones,^7,8 suggesting that renal sodium hyper-reabsorption is independent of systemic factors. Consistent with this, sodium retention is confined to the proteinuric kidney in the unilateral puromycin aminonucleoside (PAN) nephrotic model.^2,9,10There is evidence that proteases contribute to ENaC activation by cleaving the extracellular loops of the α- and γ-subunits.^11–13 Proteolytic activation of ENaC by extracellular proteases critically involves the cleavage of the γ subunit,^14–16 which probably leads to the release of a 43-residue inhibitory peptide from the ectodomain.¹⁷ Both cleaved and noncleaved channels are present in the plasma membrane,^18,19 allowing proteases such as channel activating protease 1 (CAP1/prostasin),²⁰ trypsin,²⁰ chymotrypsin,²¹ and neutrophil elastase²² to activate noncleaved channels from the extracellular side.^23,24 We hypothesized that the defective glomerular filtration barrier in nephrotic syndrome allows the filtration of ENaC-activating proteins into the tubular fluid, leading to stimulation of ENaC. The hypothesis was tested in the PAN nephrotic model in rats and with urine from patients with nephrotic syndrome.     

Association between patients' gender, age and immigrant background and use of restraint--a 2-year retrospective study at a department of emergency psychiatry

The study aimed to determine rates and types of patient restraint, and their relationship to age, gender and immigrant background. The study retrospectively examined routinely collected data and data from restraint protocols in a department of acute psychiatry over a 2-year period. Each patient is only counted once in this period, controlling for readmission. Of 960 admitted patients, 14% were exposed to the use of restraints. The rate was significantly higher among patients with immigrant background, especially in the younger age groups. Most commonly used were mechanical restraint alone for native-born patients and a combination of mechanical and pharmacological restraints for patients with immigrant background. The use of restraints decreased when patients reached 60 years. Both patients' age and immigrant background seem to have an impact on the use of restraint.     

Linkage and mutational analysis of CLCN2 in childhood absence epilepsy

In order to assess the chloride channel gene CLCN2 as a candidate susceptibility gene for childhood absence epilepsy, parametric and non-parametric linkage analysis was performed in 65 nuclear pedigrees. This provided suggestive evidence for linkage with heterogeneity: NPL score=2.3, p<0.009; HLOD=1.5, alpha=0.44. Mutational analysis of the entire genomic sequence of CLCN2 was performed in 24 unrelated patients from pedigrees consistent with linkage, identifying 45 sequence variants including the known non-synonymous polymorphism rs2228292 (G2154C, Glu718Asp) and a novel variant IVS4+12G>A. Intra-familial association analysis using the pedigrees and a further 308 parent-child trios showed suggestive evidence for transmission disequilibrium of the G2154C minor allele: AVE-PDT chi(1)2 = 5.17, p<0.03. Case-control analysis provided evidence for a protective effect of the IVS4+12G>A minor allele: chi(1)2 = 7.27, p<0.008. The 65 nuclear pedigrees were screened for three previously identified mutations shown to segregate with a variety of idiopathic generalised epilepsy phenotypes (597insG, IVS2-14del11 and G2144A) but none were found. We conclude that CLCN2 may be a susceptibility locus in a subset of cases of childhood absence epilepsy.     

The effect of gender on emotion perception in schizophrenia and bipolar disorder

OBJECTIVE: Impaired emotion perception is documented for schizophrenia, but findings have been mixed for bipolar disorder. In healthy samples females perform better than males. This study compared emotion perception in schizophrenia and bipolar disorder and investigated the effects of gender. METHOD: Visual (facial pictures) and auditory (sentences) emotional stimuli were presented for identification and discrimination in groups of participants with schizophrenia, bipolar disorder and healthy controls. RESULTS: Visual emotion perception was unimpaired in both clinical groups, but the schizophrenia sample showed reduced auditory emotion perception. Healthy males and male schizophrenia subjects performed worse than their female counterparts, whereas there were no gender differences within the bipolar group. CONCLUSION: A disease-specific auditory emotion processing deficit was confirmed in schizophrenia, especially for males. Participants with bipolar disorder performed unimpaired.     

The occurrence and characteristics of auras in a large epilepsy cohort

Objectives – Despite several studies, estimates of the frequency with which auras occur in conjunction with epilepsy continue to be imprecise. The aim of this study was to assess the occurrence and characteristics of auras in a large population‐based epilepsy cohort. Materials and methods – Subjects with verified epilepsy were recruited from population‐based twin registries in the USA, Denmark and Norway. Using a structured interview in which a list of auras was provided, subjects were asked about the warning symptoms preceding their epileptic attacks. Results – 31% of the total sample (n = 1897) and 39% of those with active epilepsy (n = 765) had experienced an aura. Six percent reported more than one type. Non‐specified auras were most frequently reported (35%), followed by somatosensory (11%) and vertiginous (11%). While the majority of those reporting auras (59%) had focal epilepsies, auras of a mostly non‐specific nature were experienced by 13% of those with generalized epilepsies. Conclusion – Auras serve an important purpose in that they may prevent seizure‐related injuries and could provide an indication as to where the seizures originate. The occurrence of auras often is underestimated, especially in children and those with learning disabilities.     

Which seizure-precipitating factors do patients with epilepsy most frequently report?

When treating patients with epilepsy, dealing with seizure-precipitating factors is a partly neglected and underestimated supplement to more traditional therapies. The aim of this study was to investigate the incidence of seizure precipitants in a large epilepsy population and to determine which precipitants patients most often reported. Study participants included twins and their family members ascertained from the Norwegian Twin Panel (NTP), the Danish Twin Registry (DTR), and the Mid-Atlantic Twin Registry (MATR). One thousand six hundred seventy-seven patients with epilepsy were identified and were asked about seizure precipitants using a closed-ended questionnaire. Fifty-three percent reported at least one seizure-precipitating factor, while 30% claimed to have experienced two or more such factors. Emotional stress, sleep deprivation, and tiredness were the three most frequently reported precipitants. Patients with generalized seizures seemed to be more sensitive to sleep deprivation and flickering light than those with partial seizures, while women with partial seizures appeared to be more prone to seizures during menstruation than women with generalized seizures. Knowledge of seizure precipitants has practical implications, not only in patient treatment and counseling, but also for diagnosis, in that it may be helpful in facilitating the appearance of interictal epileptiform discharges in EEG and ictal EEG recordings.     

Occupational contact dermatitis from Cichorium (chicory, endive) and Lactuca (lettuce)

In two cases, occupational contact dermatitis was found to be due to chicory (Cichorium) used as a salad plant. In one of the two cases, contact sensitivity to letuce (Lactuca) was also observed. The sesquiterpene lactones of the plant may be the allergens.