G. Szücs

Serum concentrations of 25-OH vitamin D in patients with systemic lupus erythematosus (SLE) are inversely related to disease activity: is it time to routinely supplement patients with SLE with vitamin D?

Background Low serum vitamin D concentrations have been reported in several autoimmune disorders. Objective To assess whether low serum vitamin D concentrations are related to disease activity of patients with systemic lupus erythematosus (SLE). Methods 378 patients from several European and Israeli cohorts were pooled and their disease activity was measured by two different methods: 278 patients had SLE disease activity-2000 (SLEDAI-2K) scores and 100 patients had European Consensus Lupus Activity Measurement (ECLAM) scores. In order to combine the two systems the scores were converted into standardised values (z-scores), enabling univariate summary statistics for the two variables (SLEDAI-2K and ECLAM). The commercial kit, LIAISON 25-OH vitamin D assay (310900-Diasorin) was used to measure serum concentration of 25-OH vitamin D in 378 patients with SLE. Results A significant negative correlation was demonstrated between the serum concentration of vitamin D and the standardised values (z-scores) of disease activity scores as measured by the SLEDAI-2K and ECLAM scales (Pearsons correlation coefficient r=−0.12, p=0.018). Conclusions In a cohort of patients with SLE originating from Israel and Europe vitamin D serum concentrations were found to be inversely related to disease activity.

Presynaptic Rat Kv1.2 Channels Suppress Synaptic Terminal Hyperexcitability Following Action Potential Invasion

Voltage‐gated K+ channels activating close to resting membrane potentials are widely expressed and differentially located in axons, presynaptic terminals and cell bodies. There is extensive evidence for localisation of Kv1 subunits at many central synaptic terminals but few clues to their presynaptic function. We have used the calyx of Held to investigate the role of presynaptic Kv1 channels in the rat by selectively blocking Kv1.1 and Kv1.2 containing channels with dendrotoxin‐K (DTX‐K) and tityustoxin‐Kα (TsTX‐Kα) respectively. We show that Kv1.2 homomers are responsible for two‐thirds of presynaptic low threshold current, whilst Kv1.1/Kv1.2 heteromers contribute the remaining current. These channels are located in the transition zone between the axon and synaptic terminal, contrasting with the high threshold K+ channel subunit Kv3.1 which is located on the synaptic terminal itself. Kv1 homomers were absent from bushy cell somata (from which the calyx axons arise); instead somatic low threshold channels consisted of heteromers containing Kv1.1, Kv1.2 and Kv1.6 subunits. Current‐clamp recording from the calyx showed that each presynaptic action potential (AP) was followed by a depolarising after‐potential (DAP) lasting around 50 ms. Kv1.1/Kv1.2 heteromers had little influence on terminal excitability, since DTX‐K did not alter AP firing. However TsTX‐Kα increased DAP amplitude, bringing the terminal closer to threshold for generating an additional AP. Paired pre‐ and postsynaptic recordings confirmed that this aberrant AP evoked an excitatory postsynaptic current (EPSC). We conclude that Kv1.2 channels have a general presynaptic function in suppressing terminal hyperexcitability during the depolarising after‐potential.

BLOCKERS OF VOLUME-ACTIVATED CL- CURRENTS INHIBIT ENDOTHELIAL CELL PROLIFERATION

Volume-activated Cl− currents (ICl,vol) and cell growth have been measured in cultured endothelial cells from bovine pulmonary artery (CPAE) in the absence and presence of compounds which block these currents. The anti-oestrogen drug tamoxifen, which efficiently arrests the growth of breast cancer cells (l), inhibits both ICl,vol and cell proliferation with IC50 of 3.8 and 4.8 μmol/l respectively. NPPB and quinine, which also block ICl,vol, inhibit the growth of CPAE cells as well. Current and cell growth were closely correlated under all these conditions. We conclude that ICl,vol might be involved in the control of endothelial cell growth and thus might be important for the modulation of vascularisation and vascular remodelling.

Action potentials and potassium currents in rat ventricular muscle during experimental diabetes

Time course of the surface electrical activity was studied in left ventricular trabeculae of Wistar rats made diabetic using streptozotocin. The action potentials were recorded in Tyrodes solution at 32 degrees C, their duration considerably increased in diabetes. By the 8th week, the prolongation was 64% at 25% of repolarization; 112% at 50% and 118% at 75%. Insulin treatment reduced the prolongation of the action potentials although a complete restoration was not achieved. 0.1 mM La3+ moderately shortened the electrical activity both in control and in diabetic trabeculae. Three mM 4-aminopyridine made the time course of control action potentials very similar to the diabetic ones while the action potentials from the diabetic animals were prolonged further to a smaller extent. Whole-cell clamp experiments in isolated ventricular myocytes (20-23 degrees C) showed a considerable decrease and a somewhat accelerated inactivation of the transient outward current (Ito) in diabetes. The steady-state inactivation and the rate of recovery from inactivation of Ito did not change. No alterations in the magnitude and voltage dependence of inward rectifier (IK1) were found around the resting membrane potential. The diabetes-related suppression of Ito explains the decreased repolarization rate of action potentials.

Survival and causes of death in 366 Hungarian patients with systemic sclerosis

Objective: Survival analysis of a series of 366 consecutive patients with systemic sclerosis (SSc). Methods: Clinical and laboratory data were evaluated from 1983 until 2005 using a standard protocol. The female/male ratio was 315/51. The mean (SD) age of the patients was 56.8 (12.2) years. The duration of disease was 12 (5–19) years with a median follow-up of 6 (3–12) years. Results: Kaplan–Meier univariate analysis showed that renal, cardiac involvement, pigmentation disturbances, malabsorption, a forced vital capacity <50%, diffuse scleroderma, presence of early malignancy, anaemia, and increased erythrocyte sedimentation rate (ESR) were signs of unfavourable prognosis, whereas anti-centromere antibodies were indicators of a good survival. In the multivariate Cox proportional hazards model the presence of diffuse scleroderma, renal involvement, coexistence of a malignant disease, and increased ESR were poor independent prognostic signs. Elderly age at the onset of disease also caused an unfavourable outcome. A total of 86 SSc-related deaths were recorded during the follow-up. Of them, 65% were attributed to cardiorespiratory manifestation of disease. Tumour associated early death was found in 12 cases (14%). Conclusions: In addition to the well-known factors influencing the outcome (diffuse subset, internal organ involvements, and inflammatory signs), the coexistence of scleroderma with a malignancy also causes a poor outcome.

Annexin II modulates volume-activated chloride currents in vascular endothelial cells

The membrane-associated, microfilament-binding protein annexin II is abundantly expressed in endothelial cells from calf pulmonary artery (CPAE cells). We have analyzed its role in the regulation of volume-activated chloride currents (ICl, vol) by loading the cells via the patch pipette with a peptide comprising the N-terminal 14 residues of annexin II. This sequence harbors the binding site for the intracellular annexin II ligand, p11, and the peptide interferes with the annexin II-p11 complex formation. Loading of a CPAE cell with this peptide caused a gradual decrease in the amplitude of ICl, vol during repetitive stimulations with a 28% hypotonic extracellular solution. This run down of the current was virtually absent in untreated cells and in cells that were loaded with a mutated 14-amino acid peptide, which has a single amino acid replacement known to result in a more than 1000 times reduced affinity for binding to p11. We conclude that annexin II-p11 complex formation is either directly or indirectly involved in the activation of ICl, vol in endothelial cells.

Activation of the volume-sensitive chloride current in vascular endothelial cells requires a permissive intracellular Ca2+ concentration

Combined patch clamp and Ca2+-measurements (Fura-2) were used to study the dependence of volume-activated Cl−-currents (ICl,vol) of endothelial cells from bovine pulmonary artery on the intracellular Ca2+-concentration [Ca2+]i. Loading the cells with high concentrations of EGTA or BAPTA via ruptured membrane patches or by preincubating them with 50 μM BAPTA-AM caused a substantial decrease of ICl,vol. This reduction was independent of the activation state of the current: the current amplitude was not only diminished if [Ca2+]i was lowered at the peak of the volume-activated current, but this low Ca2+-concentration also prevented activation of the current by a second hypotonic challenge.ICl,vol is already maximally activated at intracellular Ca2+-concentrations between 50 and 100 nmol/l, a further increase of [Ca2+]i does not affect the size of ICl,vol.These results indicate that a sustained full activation of ICl,vol in endothelial cells requires submicromolar concentrations of Ca2+, and that changes in [Ca2+]i do not modulate the current.

Mitochondrial expression of the two-pore domain TASK-3 channels in malignantly transformed and non-malignant human cells

The presence of TASK-3 channels has been described in a number of healthy and malignantly transformed cells, showing mainly intracellular distribution with relatively insignificant labelling of the cell surface membrane. In this work, immunochemical and molecular biology methods were utilised to establish the intracellular organelle whose TASK-3 expression accounts for this strong intracellular labelling using cultured melanoma and HaCaT cells. Before the immunocytochemical experiments, the presence of TASK-3 mRNA was also confirmed in melanoma cells. Comparison of the results of the TASK-3- and mitochondrion-specific labelling indicated that the TASK-3 channel subunits were strongly expressed by mitochondria in both investigated cell types. Moreover, prominent TASK-3 expression of keratinocytes could also be demonstrated in histological sections excised from the human skin. These results indicate that TASK-3 channels are present in the mitochondria in both malignantly transformed and healthy cells, suggesting that they might have roles in ensuring mitochondrial functions.

Inhibition of volume-activated chloride currents in endothelial cells by chromones

1 We have studied the effects of the reported chloride channel blocker, sodium cromoglycate, on volume‐activated Cl− currents in endothelial cells from bovine pulmonary artery by means of the whole‐ cell patch clamp technique. Cl− currents were activated by challenging the cells with a hypotonic extracellular solution of 60% of the normal osmolality. 2 Half maximal activation of the current at +95 mV occurred after exposure of the cells for 148 ± 10 s (n = 6) to hypotonic solution (HTS). At the same membrane potential but in the presence of 100 μm sodium cromoglycate (disodium‐1, 3‐bis (2′‐carboxylate‐chromone‐5′‐yloxy)‐2‐hydroxy‐propane) activation was delayed (253 ± 25 s, n = 6) and the maximal current amplitude was reduced to 63 ± 7% of the control (n=13). 3 In comparison, an equimolar concentration of NPPB (5‐nitro‐2(3‐phenyl) propylamino‐benzoic acid), another Cl− channel blocker, completely blocked the volume‐activated current in less than 20 s. 4 Sodium cromoglycate, applied at the time when the HTS‐induced current was completely activated, dose‐dependently inhibited this current with a concentration for half maximal inhibition of 310 ±70 μm. Data for nedocromil sodium were not significantly different from those for sodium cromoglycate. 5 Sodium cromoglycate, loaded into the endothelial cells via the patch pipette in ruptured patches, resulted in a decline of the HTS activated current with a time course that was compatible with diffusion of the compound from the pipette into the cell. Intracellulary applied sodium cromoglycate was also more effective and at 50 μm caused a decrease in the amplitude of the current to 25 ±6% (n= 10) of the control current. 6 It is concluded that blockade of volume‐activated Cl− currents by extracellular sodium cromoglycate may be due to an intracellular action following its permeation across the cell membrane.

The volume-activated chloride current in endothelial cells from bovine pulmonary artery is not modulated by phosphorylation

We employed the patch-clamp technique to investigate the effects of various phosphorylation pathways on activation and modulation of volume-activated Cl- currents (ICl,vol) in cultured endothelial cells from bovine pulmonary arteries (CPAE cells). Half-maximal activation ofICl,vol occurred at a hypotonicity of 27.5 ± 1.2%. Run-down of the current upon repetitive activation was less than 15% within 60 min. Stimulation of protein kinase C (PKC) by phorbol-12-myristate-13-acetate (PMA) or by (−)-indolactam did not affectICl,vol. Down regulation of PKC activity by a 24-h preincubation of the cells with 0.2 μmol/l PMA, or its inhibition by loading the cells with the specific inhibitory 19–31 pseudosubstrate peptide, did not influenceICl,vol. Trifluoperazine and tamoxifen fully blockedIcCl,vol with concentrations required for half-maximal inhibition of 3.0 and 2.4 μmol/1 respectively. This inhibitory effect is probably not mediated by the calmodulin-antagonistic action of these compounds, because it occurs at free intracellular [Ca2+] of 50 nmol/l, which are below the threshold for calmodulin activation. The tyrosine kinase inhibitor herbimycin A (1 μol/1) and genistein (100 μol/1) did not affectICl,vol Exposing CPAE cells to lysophosphatidic acid (1μmol/1), an activator of p42 MAPkinase and the focal adhesion kinase p125FAK in endothelial cells, neither evoked a Cl− current nor affectedICl,vol Neither wortmannin (10 μmol/1), an inhibitor of MAP kinases and of PI-3 kinase, nor rapamycin (0.1 mmol/1), which interferes with the p70S6 kinase pathway, affectedICl,vol Exposure of CPAE cells to heat or Na-arsenite, both activators of a recently discovered stress-activated tyrosine phosphorylation pathway, neither activated a current nor affected the hypotonic solution-induced Cl− current. We conclude that none of the studied phosphorylation pathways is essential for the activation of the Cl− current induced by hypotonicity.