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Rapamycin, an inhibitor of the serine/threonine kinase mammalian target of rapamycin (mTOR), is a widely used immunosuppressive drug. Rapamycin affects the function of dendritic cells (DCs), antigen-presenting cells participating in the initiation of primary immune responses and the establishment of immunological memory. Voltage-gated [K.sup.+] (Kv) channels are expressed in and impact on the function of DCs. The present study explored whether rapamycin influences Kv channels in DCs. To this end, DCs were isolated from murine bone marrow and ion channel activity was determined by whole cell patch clamp. To more directly analyze an effect of mTOR on Kv channel activity, Kv1.3 and Kv1.5 were expressed in Xenopus oocytes with or without the additional expression of mTOR and voltage-gated currents were determined by dual-electrode voltage clamp. As a result, preincubation with rapamycin (0-50 nM) led to a gradual decline of Kv currents in DCs, reaching statistical significance within 6 h and 50 nM of rapamycin. Rapamycin accelerated Kv channel inactivation. Coexpression of mTOR upregulated Kv1.3 and Kv1.5 currents in Xenopus oocytes. Furthermore, mTOR accelerated Kv1.3 channel activation and slowed down Kv1.3 channel inactivation. In conclusion, mTOR stimulates Kv channels, an effect contributing to the immunomodulating properties of rapamycin in DCs. mammalian target of rapamycin; immunosuppression; cell membrane potential; Kv1.3; Kv1.5; macrophages doi: 10.1152/ajpcell.00367.2010.

Previous studies have shown that pharmacological inhibition of the phosphoinositol-3 (PI3) kinase disrupts the activation of mast cells. Through phosphoinositide-dependent kinase PDK1, PI3 kinase activates the serum- and glucocorticoid-inducible kinase 3 (SGK3). The present study explored the role of SGK3 in mast cell function. Mast cells were isolated and cultured from bone marrow (BMMCs) of gene-targeted mice lacking SGK3 ([sgk3.sup.-/-]) and their wild-type littermates ([sgk3.sup.+/+]). BMMC numbers in the ear conch were similar in both genotypes. Stimulation with IgE and cognate antigen triggered the release of intracellular [Ca.sup.2+] and entry of extracellular [Ca.sup.2+]. Influx of extracellular [Ca.sup.2+] but not [Ca.sup.2+] release from intracellular stores was significantly blunted in [sgk3.sup.-/-] BMMCs compared with [sgk3.sup.+/+] BMMCs. Antigen stimulation further led to a rapid increase of a [K.sup.+]-selective conductance in [sgk3.sup.+/+] BMMCs, an effect again blunted in [sgk3.sup.-/-] BMMCs. In contrast, the [Ca.sup.2+] ionophore ionomycin activated [K.sup.+] currents to a similar extent in [sgk3.sup.-/-] and in [sgk3.sup.+/+] BMMCs. [beta]-Hexosaminidase release, triggered by antigen stimulation, was also significantly decreased in [sgk3.sup.-/-] BMMCs. IgE-dependent anaphylaxis measured as a sharp decrease in body temperature upon injection of DNP-HSA antigen was again significantly blunted in [sgk3.sup.-/-] compared with [sgk3.sup.+/+] mice. Serum histamine levels measured 30 rain after induction of an anaphylactic reaction were significantly lower in [sgk3.sup.-/-] than in [sgk3.sup.+/+] mice. In conclusion, both in vitro and in vivo function of BMMCs are impaired in gene targeted mice lacking SGK3. Thus SGK3 is critical for proper mast cell function. allergy; anaphylaxis; calcium ion channels; degranulation; potassium ion channels; [K.sub.ca] 3.1; phosphoinositol-3 kinase doi: 10.1152/ajpcell.00539.2009.

Eryptosis or apoptosis-like death of erythrocytes is characterized by phosphatidylserine exposure and erythrocyte shrinkage, both typical features of nucleated apoptotic cells. Eryptosis is triggered by activation of nonselective [Ca.sup.2+]-permeable cation channels with subsequent entry of [Ca.sup.2+] and stimulation of [Ca.sup.2+]-sensitive scrambling of the cell membrane. The channels are activated and thus eryptosis is triggered by [Cl.sup.-] removal, osmotic shock, oxidative stress, or glucose deprivation. The present study has been performed to compare cation channel activity and susceptibility to eryptosis in neonatal and adult erythrocytes. Channel activity was determined by patch-clamp analysis, cytosolic [Ca.sup.2+] activity by fluo-3 fluorescence, phosphatidylserine exposure by FITC-labeled annexin V binding, and cell shrinkage by decrease in forward scatter in fluorescence-activated cell sorting analysis. Prostaglandin [E.sub.2]([PGE.sub.2]) formation, cation channel activity, [Ca.sup.2+] entry, annexin V binding, and decreased forward scatter were triggered by removal of [Cl.sup.-] in both adult and neonatal erythrocytes. The effects were, however, significantly blunted in neonatal erythrocytes. Osmotic shock, [PGE.sub.2], and platelet-activating factor similarly increased annexin V binding and decreased forward scatter, effects again significantly reduced in neonatal erythrocytes. On the other hand, spontaneous and oxidative (addition of tert-butylperoxide) stress-induced eryptosis was significantly larger in neonatal erythrocytes. In conclusion, cation channel activity, [Ca.sup.2+] leakage, and thus channel-dependent triggering of eryptosis are blunted, whereas spontaneous and oxidative stress-induced eryptosis is more pronounced in neonatal erythrocytes. annexin V; osmotic cell shrinkage; calcium; apoptosis

Infection of human erythrocytes with the malaria parasite Plasmodium falciparum induces new permeability pathways (NPPs) in the host cell membrane. Isotopic flux measurements demonstrated that the NPP are permeable to a wide variety of molecules, thus allowing uptake of nutrients and release of waste products. Recent patch-clamp recordings demonstrated the infection-induced up-regulation of an inwardly and an outwardly rectifying [Cl.sup.-] conductance. The present experiments have been performed to explore the sensitivity to cell volume and the organic osmolyte permeability of the two conductances. It is shown that the outward rectifier has a high relative lactate permeability ([P.sub.lactate]/[P.sub.Cl] = 0.4). Sucrose inhibited the outward-rectifier and abolished the infection-induced hemolysis in isosmotic sorbitol solution but had no or little effect on the inward-rectifier. Furosemide and NPPB blocked the outward-rectifying lactate current and the sorbitol hemolysis with I[C.sub.50]s in the range of 0.1 and 1 [micro]M, respectively. In contrast, the I[C.sub.50]s of NPPB and furosemide for the inward-rectifying current were >10 [micro]M. Osmotic cell-shrinkage inhibited the inwardly but not the outwardly rectifying conductance. In conclusion, the parasite-induced outwardly-rectifying anion conductance allows permeation of lactate and neutral carbohydrates, whereas the inward rectifier seems largely impermeable to organic solutes. All together, these data should help to resolve ongoing controversy regarding the number of unique channels that exist in P. falciparum-infected erythrocytes. KEY WORDS: plasmodium falciparum * new permeability pathways * osmolyte channel * red blood cells * patch-clamp

Bone-marrow-derived mast cells are matured from bone marrow cells in medium containing 20% fetal calf serum (FCS), interleukin (IL)-3 and stem-cell factor (SCF) and are used as in vitro models to study mast cells (MC) and their role in health and disease. In vivo, however, BM-derived hematopoietic stem cells account for only a fraction of MC; the majority of MC in vivo are and remain tissue resident. In this study we established a side-by-side culture with BMMC, fetal skin MC (FSMC) or fetal liver MC (FLMC) for comparative studies to identify the best surrogates for mature connective tissue MC (CTMC). All three MC types showed comparable morphology by histology and MC phenotype by flow cytometry. Heterogeneity was detected in the transcriptome with the most differentially expressed genes in FSMC compared to BMMC being Hdc and Tpsb2. Expression of ST2 was highly expressed in BMMC and FSMC and reduced in FLMC, diminishing their secretion of type 2 cytokines. Higher granule content, stronger response to FcεRI activation and significantly higher release of histamine from FSMC compared to FLMC and BMMC indicated differences in MC development in vitro dependent on the tissue of origin. Thus, tissues of origin imprint MC precursor cells to acquire distinct phenotypes and signatures despite identical culture conditions. Fetal-derived MC resemble mature CTMC, with FSMC being the most developed. [ABSTRACT FROM AUTHOR]

Background/Aims: Janus kinase 3 (JAK3), a tyrosine kinase mainly expressed in hematopoietic cells, participates in the signaling stimulating cell proliferation. The kinase is expressed in dendritic cells (DCs), antigen presenting cells involved in the initiation and regulation of antigen-specific T-cell responses. Dendritic cell function is regulated by cytosolic Ca2+ activity ([Ca2+]i). Mediators increasing [Ca2+] in DCs include ATP and the chemokine receptor CXCR4 ligand CXCL12. The present study explored, whether JAK3 participates in the regulation of [Ca2+] in DCs. Methods: Fura-2 fluorescence was employed to determine [Ca2+]i, and whole cell patch clamp to decipher electrogenic transport in immature DCs isolated from bone marrow of JAK3-knockout (jak3-/-) or wild-type mice (jak3+/+). Results: Without treatment, [Ca2+] was similar in jak3-/- and jak3+/+ DCs. Addition of ATP (100 |JM) was followed by transient increase of [Ca2+] reflecting Ca2+ release from intracellular stores, an effect significantly less pronounced injak3-/' DCs than injak3+/+ DCs. CXCL12 administration was followed by a sustained increase of [Ca2+] reflecting receptor operated Ca2+ entry, an effect significantly less rapid in jak3-/- DCs than in jak3+/+ DCs. In addition, the Ca2+ release-activated Ca2+ channel (CRAC) current triggered by IP3-induced Ca2+ store depletion and CXCL12 was significantly higher in DCs from jak3+/+ mice than in jak3-/- mice. Inhibition of sarcoendoplasmatic reticulum Ca2+- ATPase (SERCA) by thapsigargin (1 |JM) in the absence of extracellular Ca2+ was followed by a transient increase of [Ca2+] reflecting Ca2+ release from intracellular stores, and subsequent readdition of extracellular Ca2+ in the continued presence of thapsigargin was followed by a sustained increase of [Ca2+] reflecting store operated Ca2+ entry (SOCE). Both, Ca2+ release from intracellular stores and SOCE were again significantly lower in jak3-/- DCs than in jak3+/+ DCs. Pretreatment of jak3+/+ DCs with JAK inhibitor WHI-P154 (22 |JM, 10 minutes or 24 hours) significantly blunted both thapsigargin induced Ca2+ release and subsequent SOCE. Abrupt replacement of Na+ containing (130 mM) and Ca2+ free (0 mM) extracellular bath by Na+ free (0 mM) and Ca2+ containing (2 mM) extracellular bath increased [Ca2+] reflecting Na+/Ca2+ exchanger activity, an effect again significantly less pronounced in jak3-/- DCs than in jak3+/+ DCs. Conclusions: JAK3 deficiency is followed by down-regulation of cytosolic Ca2+ release, receptor and store operated Ca2+ entry and Na+/Ca2+ exchanger activity in DCs. [ABSTRACT FROM AUTHOR]

Background/Aims: The WNK-dependent STE20/SPS1-related proline/alanine-rich kinase SPAK participates in the regulation of NaCl and Na+,K+,2Cl- cotransport and thus renal salt excretion. The present study explored whether SPAK has similarly the potential to regulate the epithelial Na+ channel (ENaC). Methods: ENaC was expressed in Xenopus oocytes with or without additional expression of wild type SPAK, constitutively active T233ESPAK, WNK insensitive T233ASPAK or catalytically inactive D212ASPAK, and ENaC activity estimated from amiloride (50 µM) sensitive current (Iamil) in dual electrode voltage clamp experiments. Moreover, Ussing chamber was employed to determine Iamil in colonic tissue from wild type mice (spakwt/wt) and from gene targeted mice carrying WNK insensitive SPAK (spaktg/tg Results: Iamil was observed in ENaC-expressing oocytes, but not in water-injected oocytes. In ENaC expressing oocytes Iamil was significantly increased following coexpression of wild-type SPAK and T233ESPAK, but not following coexpression of T233ASPAK or D212ASPAK. Colonic Iamil was significantly higher in spakw wtthan in spaktg/tg mice. Conclusion: SPAK has the potential to up-regulate ENaC. [ABSTRACT FROM AUTHOR]

USP18 (Ubiquitin-like specific protease 18) is an enzyme cleaving ubiquitin from target proteins. USP18 plays a pivotal role in antiviral and antibacterial immune responses. On the other hand, ubiquitination participates in the regulation of several ion channels and transporters. USP18 sensitivity of transporters has, however, never been reported. The present study thus explored, whether USP18 modifies the activity of the peptide transporters PEPT1 and PEPT2, and whether the peptide transporters are sensitive to the ubiquitin ligase Nedd4-2. To this end, cRNA encoding PEPT1 or PEPT2 was injected into Xenopus laevis oocytes without or with additional injection of cRNA encoding USP18. Electrogenic peptide (glycine-glycine) transport was determined by dual electrode voltage clamp. As a result, in Xenopus laevis oocytes injected with cRNA encoding PEPT1 or PEPT2, but not in oocytes injected with water or with USP18 alone, application of the dipeptide gly-gly (2 mM) was followed by the appearance of an inward current (Igly-gly). Coexpression of USP18 significantly increased Igly-gly in both PEPT1 and PEPT2 expressing oocytes. Kinetic analysis revealed that coexpression of USP18 increased maximal Igly-gly. Conversely, overexpression of the ubiquitin ligase Nedd4-2 decreased Igly-gly. Coexpression of USP30 similarly increased Igly-gly in PEPT1 expressing oocytes. In conclusion, USP18 sensitive cellular functions include activity of the peptide transporters PEPT1 and PEPT2. [ABSTRACT FROM AUTHOR]

Background/Aims: Janus kinase-3 (JAK3) is activated during energy depletion. Energy-consuming pumps include the Na+/K+-ATPase. The present study explored whether JAK3 regulates Na+/K+-ATPase in dendritic cells (DCs). Methods: Ouabain (100 µM)-sensitive (Iouabain) and K+-induced (Ipump) outward currents were determined by utilizing whole cell patch-clamp, Na+/K+-ATPase α1-subunit mRNA levels by RT-PCR, Na+/K+-ATPase protein abundance by flow cytometry or immunofluorescence, and cellular ATP by luciferase-assay in DCs from bone marrow of JAK3-knockout (jak3-/-) or wild-type mice (jak3+/+). Ipump was further determined by voltage clamp in Xenopus oocytes expressing JAK3, active A568VJAK3 or inactive K851AJAK3. Results: Na+/K+-ATPase α1-subunit mRNA and protein levels, as well as Ipump and Iouabain were significantly higher in jak3-/-DCs than in jak3+/+DCs. Energy depletion by 4h pre-treatment with 2,4-dinitro-phenol significantly decreased Ipump in jak3+/+ DCs but not in jak3-/-DCs. Cellular ATP was significantly lower in jak3-/-DCs than in jak3+/+DCs and decreased in both genotypes by 2,4-dinitro-phenol, an effect significantly more pronounced in jak3-/-DCs than in jak3+/+DCs and strongly blunted by ouabain in both jak3+/+ and jak3-/-DCs. Ipump and Iouabain in oocytes were decreased by expression of JAK3 and of A568VJAK3 but not of K851AJAK3. JAK3 inhibitor WHI-P154 (4-[(3'-bromo-4'-hydroxyphenyl)amino]-6,7-dimethoxyquinazoline, 22 μM) enhanced Ipump and Iouabain in JAK3 expressing oocytes. The difference between A568VJAK3 and K851AJAK3 expressing oocytes was virtually abrogated by actinomycin D (50 nM). Conclusions: JAK3 down-regulates Na+/K+-ATPase activity, an effect involving gene expression and profoundly curtailing ATP consumption. [ABSTRACT FROM AUTHOR]

Gene variants of the leucine-rich repeat kinase 2 (LRRK2) are associated with susceptibility to Parkinson's disease (PD). Besides brain and periphery, LRRK2 is expressed in various immune cells including dendritic cells (DCs), antigen-presenting cells linking innate and adaptive immunity. However, the function of LRRK2 in the immune system is still incompletely understood. Here, Ca2+-signaling was analyzed in DCs isolated from gene-targeted mice lacking lrrk2 (Lrrk2-/-) and their wild-type littermates (Lrrk2+/+). According to Western blotting, Lrrk2 was expressed in Lrrk2+/+ DCs but not in Lrrk2-/-DCs. Cytosolic Ca2+ levels ([Ca2+]i) were determined utilizing Fura-2 fluorescence and whole cell currents to decipher electrogenic transport. The increase of [Ca2+]i following inhibition of sarcoendoplasmatic Ca2+-ATPase with thapsigargin (1 mM) in the absence of extracellular Ca2+ (Ca2+-release) and the increase of [Ca2+]i following subsequent readdition of extracellular Ca2+ (SOCE) were both significantly larger in Lrrk2-/- than in Lrrk2+/+ DCs. The augmented increase of [Ca2+]i could have been due to impaired Ca2+ extrusion by K+-independent (NCX) and/or K+-dependent (NCKX) Na+/Ca2+-exchanger activity, which was thus determined from the increase of [Ca2+]i, (D[Ca2+]i), and current following abrupt replacement of Na+ containing (130 mM) and Ca2+ free (0 mM) extracellular perfusate by Na+ free (0mM) and Ca2+ containing (2 mM) extracellular perfusate. As a result, both slope and peak of D[Ca2+]i as well as Na+/Ca2+ exchanger-induced current were significantly lower in Lrrk2-/- than in Lrrk2+/+ DCs. A 6 or 24 hour treatment with the LRRK2 inhibitor GSK2578215A (1 µM) significantly decreased NCX1 and NCKX1 transcript levels, significantly blunted Na+/Ca2+- exchanger activity, and significantly augmented the increase of [Ca2+]i following Ca2+-release and SOCE. In conclusion, the present observations disclose a completely novel functional significance of LRRK2, i.e., the up-regulation of Na+/Ca2+ exchanger transcription and activity leading to attenuation of Ca2+-signals in DCs. [ABSTRACT FROM AUTHOR]

Background/Aims: OSR1 (oxidative-stress-responsive kinase 1) participates in the regulation of renal tubular ion transport, cell volume and blood pressure. Whether OSR1 contributes to the regulation of organic solute transport remained; however, elusive. The present study thus explored the OSR1 sensitivity of the peptide transporters PEPT1 and PEPT2. Methods: cRNA encoding PEPT1 or PEPT2 were injected into Xenopus oocytes without or with additional injection of cRNA encoding wild-type OSR1, WNK1 insensitive inactive T185AOSR1, constitutively active T185EOSR1, and catalytically inactive D164AOSR1. Electrogenic peptide (glycine-glycine) transport was determined by dual electrode voltage clamp, the abundance of hemagglutinin-tagged PEPT2 (PEPT2-HA) by chemiluminescence. Results: In Xenopus oocytes injected with cRNA encoding PEPT1 or PEPT2, but not in oocytes injected with water, the dipeptide gly-gly (2 mM) generated an appreciable inward current (Igly-gly). Coexpression of OSR1 significantly decreased Igly-gly in both PEPT1 and PEPT2 expressing oocytes. The effect of OSR1 coexpression on Igly-gly in PEPT1 expressing oocytes was mimicked by coexpression of T185EOSR1, but not of D164AOSR1 or T185AOSR1. Kinetic analysis revealed that coexpression of OSR1 decreased maximal Igly-gly. OSR1 further decreased the PEPT2-HA protein abundance in the cell membrane. Conclusion: OSR1 has the capacity to downregulate the peptide transporters PEPT1 and PEPT2 by decreasing the carrier protein abundance in the cell membrane. © 2014 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Background/Aims: The kinases SPAK (SPS1-related proline/alanine-rich kinase) and OSR1 (oxidative stress-responsive kinase 1) participate in the regulation of the NaCl cotransporter NCC and the Na+,K+,2Cl- cotransporter NKCC2. The kinases are regulated by WNK (with-no-K[Lys]) kinases. Mutations of genes encoding WNK kinases underly Gordon's syndrome, a monogenic disease leading to hypertension and hyperkalemia. WNK kinases further regulate the renal outer medullary K+ channel ROMK1. The present study explored, whether SPAK and/or OSR1 have similarly the potential to modify the activity of ROMK1. Methods: ROMK1 was expressed in Xenopus oocytes with or without additional expression of wild-type SPAK, constitutively active T233ESPAK, catalytically inactive D212ASPAK, wild-type OSR1, constitutively active T185EOSR1 and catalytically inactive D164AOSR1. Channel activity was determined utilizing dual electrode voltage clamp and ROMK1 protein abundance in the cell membrane utilizing chemiluminescence of ROMK1 containing an extracellular hemagglutinin epitope (ROMK1-HA). Results: ROMK1 activity and ROMK1-HA protein abundance were significantly down-regulated by wild-type SPAK and T233ESPAK, but not by D212ASPAK. Similarly, ROMK1 activity and ROMK1-HA protein abundance were significantly down-regulated by wild-type OSR1 and T185EOSR1, but not by D164AOSR1. Conclusion: ROMK1 protein abundance and activity are down-regulated by SPAK and OSR1. © 2014 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]