Conformation-specific Synthetic Antibodies Discriminate Multiple Functional States of the Ion Channel CorA

CorA, the primary magnesium ion channel in prokaryotes and archaea, is a prototypical homopentameric ion channel that undergoes ion-dependent conformational transitions. CorA adopts five-fold symmetric non-conductive states in the presence of high concentrations of Mg2+, and highly asymmetric flexible states in its complete absence. However, the latter were of insufficient resolution to be thoroughly characterized. In order to gain additional insights into the relationship between asymmetry and channel activation, we exploited phage display selection strategies to generate conformation-specific synthetic antibodies (sABs) against CorA in the absence of Mg2+. Two sABs from these selections, C12 and C18, showed different degrees of Mg2+-sensitivity. Through structural, biochemical, and biophysical characterization, we found the sABs are both conformation-specific but probe different features of the channel under open-like conditions. C18 is highly specific to the Mg2+-depleted state of CorA and through negative-stain electron microscopy (ns-EM), we show sAB binding reflects the asymmetric arrangement of CorA protomers in Mg2+-depleted conditions. We used X-ray crystallography to determine a structure at 2.0 Å resolution of sAB C12 bound to the soluble N-terminal regulatory domain of CorA. The structure shows C12 is a competitive inhibitor of regulatory magnesium binding through its interaction with the divalent cation sensing site. We subsequently exploited this relationship to capture and visualize asymmetric CorA states in different [Mg2+] using ns-EM. We additionally utilized these sABs to provide insights into the energy landscape that governs the ion-dependent conformational transitions of CorA.

Crosstalk Between CD11b and Piezo1 Mediates Macrophage Responses to Mechanical Cues

Macrophages are versatile cells of the innate immune system that perform diverse functions by responding to dynamic changes in their microenvironment. While the effects of soluble cues, including cytokines and chemokines, have been widely studied, the effects of physical cues, including mechanical stimuli, in regulating macrophage form and function are less well understood. In this study, we examined the effects of static and cyclic uniaxial stretch on macrophage inflammatory and healing activation. We found that cyclic stretch altered macrophage morphology and responses to IFNγ/LPS and IL4/IL13. Interestingly, we found that both static and cyclic stretch suppressed IFNγ/LPS induced inflammation. In contrast, IL4/IL13 mediated healing responses were suppressed with cyclic but enhanced with static stretch conditions. Mechanistically, both static and cyclic stretch increased expression of the integrin CD11b (αM integrin), decreased expression of the mechanosensitive ion channel Piezo1, and knock down of either CD11b or Piezo1 through siRNA abrogated stretch-mediated changes in inflammatory responses. Moreover, we found that knock down of CD11b enhanced the expression of Piezo1, and conversely knock down of Piezo1 enhanced CD11b expression, suggesting the potential for crosstalk between integrins and ion channels. Finally, stretch-mediated differences in macrophage activation were also dependent on actin, since pharmacological inhibition of actin polymerization abrogated the changes in activation with stretch. Together, this study demonstrates that the physical environment synergizes with biochemical cues to regulate macrophage morphology and function, and suggests a role for CD11b and Piezo1 crosstalk in mechanotransduction in macrophages.

Bicarbonate permeation through anion channels: its role in health and disease

Many anion channels, frequently referred as Cl^- channels, are permeable to different anions in addition to Cl^-. As the second-most abundant anion in the human body, HCO₃^- permeation via anion channels has many important physiological roles. In addition to its classical role as an intracellular pH regulator, HCO₃^- also controls the activity and stability of dissolved proteins in bodily fluids such as saliva, pancreatic juice, intestinal fluid, and airway surface liquid. Moreover, HCO₃^- permeation through these channels affects membrane potentials that are the driving forces for transmembrane transport of solutes and water in epithelia and affect neuronal excitability in nervous tissue. Consequently, aberrant HCO₃^- transport via anion channels causes a number of human diseases in respiratory, gastrointestinal, genitourinary, and neuronal systems. Notably, recent studies have shown that the HCO₃^- permeabilities of several anion channels are not fixed and can be altered by cellular stimuli, findings which may have both physiological and pathophysiological significance. In this review, we summarize recent progress in understanding the molecular mechanisms and the physiological roles of HCO₃^- permeation through anion channels. We hope that the present discussions can stimulate further research into this very important topic, which will provide the basis for human disorders associated with aberrant HCO₃^- transport.

Aging alters Hv1-mediated microglial polarization and enhances neuroinflammation after peripheral surgery

Perioperative neurocognitive disorders have been widely recognized as common adverse events after surgical intervention. Aging is one of the most important independent risk factors for worsened cognitive outcome, and this deterioration is linked to exacerbated microglia-mediated neuroinflammation in the aged brain. Under pathological stimulation, microglia are capable of polarizing toward proinflammatory M1 and anti-inflammatory M2 phenotypes. In the present study, we examined how aging affects microglial responses and neuroinflammation following peripheral surgery. Adult (2-3 months) and aged (18 months old) male C57/BL6 mice were subjected to tibial fracture or sham surgery. Aged mice exhibited higher level of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in the hippocampus. The expression of synaptic protein synaptophysin (SYP) was also markedly reduced in the aged brain after the surgery. Both adult and aged mice showed significant increases in M1 microglial polarization (CD16/32). In contrast, tibial fracture surgery induced a decreased M2 microglial polarization (CD206, Ym1/2, Arg1) in aged brain but enhanced M2 microglial polarization in adult brain. Aged mice have upregulated voltage-gated proton channel (Hv1) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit expression compared with adult mice. The percentage of CD16/32-positive M1 microglia colabeling with Hv1 was higher in aged mice after tibial fracture surgery. Thus, Hv1/NADPH oxidase upregulation in the aged brain may shift the dynamic equilibrium of microglial activation toward M1 polarization and exaggerate postoperative neuroinflammatory responses after peripheral surgical intervention.

[Research advances in the functional roles of ion channels in immune cells and immune response]

Ion channels are a widespread class of membrane proteins that help establish and control cell membrane potential by allowing the passive diffusion of inorganic ions with high specificity through cell membrane. They are widely distributed in various cells and tissues, and their normal structure and function are of fundamental importance for all living organisms. The rapid advances in molecular cloning, protein structure analysis, patch clamp recordings and other technologies have greatly promoted the research on the biophysical and molecular properties of ion channels, and made significant progress in the study of the relationship between ion channels and pathophysiology as well. The immune system is made up of immune cells and organs that work together to protect the body and respond to infection and disease. Remarkably, recent basic and clinical research has revealed that ion channels are frequently and abundantly expressed in immune cells and have crucial roles in immune cell development and immune response. This review summarized recent progress in the roles of ion channels in immune cells, including the expression and regulation of ion channels in immune cells, the effects of ion flux mediated by ion channels on lymphocyte development, and functional roles of ion channels in both innate and adaptive immune responses. We also discussed some unresolved and insufficiently addressed issues in the current research, so as to provide an informative reference for better understanding the functional roles of ion channels in the immune system and further elucidation of their function from a physiological and pathological point of view.

Antibodies and venom peptides: new modalities for ion channels

Ion channels play fundamental roles in both excitable and non-excitable tissues and therefore constitute attractive drug targets for myriad neurological, cardiovascular and metabolic diseases as well as for cancer and immunomodulation. However, achieving selectivity for specific ion channel subtypes with small-molecule drugs has been challenging, and there currently is a growing trend to target ion channels with biologics. One approach is to improve the pharmacokinetics of existing or novel venom-derived peptides. In parallel, after initial studies with polyclonal antibodies demonstrated the technical feasibility of inhibiting channel function with antibodies, multiple preclinical programmes are now using the full spectrum of available technologies to generate conventional monoclonal and engineered antibodies or nanobodies against extracellular loops of ion channels. After a summary of the current state of ion channel drug discovery, this Review discusses recent developments using the purinergic receptor channel P2X purinoceptor 7 (P2X7), the voltage-gated potassium channel KV1.3 and the voltage-gated sodium channel NaV1.7 as examples of targeting ion channels with biologics.

Small fiber neuropathies

PURPOSE OF REVIEW

This article reviews the clinical, neurophysiologic, and neuropathologic findings in patients presenting with small fiber neuropathies. Emphasis is placed on recent updates to the literature, but also on understanding the differential diagnosis and initial evaluation of patients with small fiber neuropathy.

RECENT FINDINGS

There have been several updates in the literature about diseases associated with small fiber neuropathy. First, treatment-induced neuropathy in diabetes mellitus is an iatrogenic small fiber neuropathy linked to overly rapid correction in blood glucose levels in the setting of chronic hyperglycemia. Second, several novel mutations to sodium channels have been identified in patients presenting with idiopathic small fiber neuropathy that may significantly alter our understanding and future treatment of small fiber neuropathy. Third, antibodies against voltage-gated potassium channels appear to be associated with a much higher incidence of pain than would be expected, although the mechanism has not been established. Fourth, the link between glucose dysregulation, metabolic syndrome, and neuropathy continues to grow. Finally, several other disorders, including postural orthostatic tachycardia syndrome, have been postulated to be associated with small fiber neuropathies.

SUMMARY

Small fiber neuropathies are a heterogeneous group of disorders that may present with a variety of sensory or autonomic symptoms. Recent reports highlight a number of new causes of small fiber neuropathy that continue to reduce the number of remaining idiopathic cases.

Molecular and cellular mechanisms underlying anti-neuronal antibody mediated disorders of the central nervous system

Over the last decade multiple autoantigens located on the plasma membrane of neurons have been identified. Neuronal surface antigens include molecules directly involved in neurotransmission and excitability. Binding of the antibody to the antigen may directly alter the target protein's function, resulting in neurological disorders. The often striking reversibility of symptoms following early aggressive immunotherapy supports a pathogenic role for autoantibodies to neuronal surface antigens. In order to better understand and treat these neurologic disorders it is important to gain insight in the underlying mechanisms of antibody pathogenicity. In this review we discuss the clinical, circumstantial, in vitro and in vivo evidence for neuronal surface antibody pathogenicity and the possible underlying cellular and molecular mechanisms. This review shows that antibodies to neuronal surface antigens are often directed at conformational epitopes located in the extracellular domain of the antigen. The conformation of the epitope can be affected by specific posttranslational modifications. This may explain the distinct clinical phenotypes that are seen in patients with antibodies to antigens that are expressed throughout the brain. Furthermore, it is likely that there is a heterogeneous antibody population, consisting of different IgG subtypes and directed at multiple epitopes located in an immunogenic region. Binding of these antibodies may result in different pathophysiological mechanisms occurring in the same patient, together contributing to the clinical syndrome. Unraveling the predominant mechanism in each distinct antigen could provide clues for therapeutic interventions.

Generation of antibodies that are externally acting isoform-specific inhibitors of ion channels

There is demand for isoform-specific ion channel inhibitors as tools to investigate the biology of -endogenous ion channels and validate them as targets in drug discovery programs. There is also hope that such inhibitors may be new therapeutic agents or provide the foundation for such agents. However, in practice, it is commonly experienced that inhibitors lack sufficient specificity, fail to distinguish between members of a class of ion channel, or have other (non-ion channel) off-target effects. Due to their extraordinary specificity, antibodies offer a potentially attractive strategy for overcoming these problems. Inhibitory antibodies acting at the extracellular face of ion channels are particularly attractive because there is enhanced possibility for specificity and intracellular delivery methods are not required. Here we describe experience with such an antibody approach and methodology for generating agents based on anti-peptide polyclonal antibodies.

Quantification of uncoupling protein 2 reveals its main expression in immune cells and selective up-regulation during T-cell proliferation

Uncoupling protein 2 (UCP2) is an inner mitochondrial membrane protein. Although the protein was discovered in 1997, its function and even its tissue distribution are still under debate. Here we present a quantitative analysis of mRNA and protein expression in various mice tissues, revealing that UCP2 is mainly expressed in organs and cells associated with the immune system. Although the UCP2 gene is present in the brain, as demonstrated using quantitative RT-PCR, the protein was not detectable in neurons under physiological conditions. Instead, we could detect UCP2 in microglia, which act in the immune defense of the central nervous system. In lymphocytes, activation led to a ten-fold increase of UCP2 protein expression simultaneously to the increase in levels of other mitochondrial proteins, whereas lymphocyte re-stimulation resulted in the selective increase of UCP2. The highest detected level of UCP2 expression in stimulated T-cells (0.54 ng/(µg total cellular protein)) was approximately 200 times lower than the level of UCP1 in brown adipose tissue from room temperature acclimated mice. Both the UCP2 expression pattern and the time course of up-regulation in stimulated T-cells imply UCP2’s involvement in the immune response, probably by controlling the metabolism during cell proliferation.

Monoclonal antibody, but not synthetic peptide, targeting the ectodomain of influenza B virus M2 proton channel has antiviral activity

The proton channels of influenza A virus (A/M2) and influenza B virus (BM2) are essential for viral replication. Previously we have shown that monoclonal antibodies targeting the ectodomain of the A/M2 proton channel have antiviral activity in vitro. In this study, we generated both monoclonal antibody and phage displayed peptide against the eight amino acids comprising the ectodomain of the BM2 proton channel and investigated their antiviral activities in vitro. A cytopathic assay showed that the monoclonal antibody potently protected MDCK cells from homologous, but not heterologous, virus infections. A plaque forming assay showed that viral replication was not completely neutralized, but greatly inhibited, by the monoclonal antibody. In contrast, no antiviral activity was observed for the synthetic native or engineered peptides. These results indicate that antibody targeting the M2 proton channel is a promising therapeutic candidate for treating influenza virus infections, and that antibody structure is important for antiviral activity.

HVCN1 modulates BCR signal strength via regulation of BCR-dependent generation of reactive oxygen species

Voltage-gated proton currents regulate generation of reactive oxygen species (ROS) in phagocytic cells. In B cells, stimulation of the B cell antigen receptor (BCR) results in the production of ROS that participate in B cell activation, but the involvement of proton channels is unknown. We report here that the voltage-gated proton channel HVCN1 associated with the BCR complex and was internalized together with the BCR after activation. BCR-induced generation of ROS was lower in HVCN1-deficient B cells, which resulted in attenuated BCR signaling via impaired BCR-dependent oxidation of the tyrosine phosphatase SHP-1. This resulted in less activation of the kinases Syk and Akt, impaired mitochondrial respiration and glycolysis and diminished antibody responses in vivo. Our findings identify unanticipated functions for proton channels in B cells and demonstrate the importance of ROS in BCR signaling and downstream metabolism.

Comparative analysis of uncoupling protein 4 distribution in various tissues under physiological conditions and during development

UCP4 is a member of the mitochondrial uncoupling protein subfamily and one of the three UCPs (UCP2, UCP4, UCP5), associated with the nervous system. Its putative functions include thermogenesis, attenuation of reactive oxidative species (ROS), regulation of mitochondrial calcium concentration and involvement in cell differentiation and apoptosis. Here we investigate UCP4's subcellular, cellular and tissue distribution, using an antibody designed specially for this study, and discuss the findings in terms of the protein's possible functions. Western blot and immunohistochemistry data confirmed that UCP4 is expressed predominantly in the central nervous system (CNS), as previously shown at mRNA level. No protein was found in heart, spleen, stomach, intestine, lung, thymus, muscles, adrenal gland, testis and liver. The reports revealing UCP4 mRNA in kidney and white adipose tissue were not confirmed at protein level. The amount of UCP4 varies in the mitochondria of different brain regions, with the highest protein content found in cortex. We show that UCP4 is present in fetal murine brain tissue as early as embryonic days 12-14 (E12-E14), which coincides with the beginning of neuronal differentiation. The UCP4 content in mitochondria decreases as the age of mice increases. UCP4 preferential expression in neurons and its developmental expression pattern under physiological conditions may indicate a specific protein function, e.g. in neuronal cell differentiation.

Vaccine prospects for amebiasis

Entamoeba histolytica is a eukaryotic protozoan parasite and is the causative agent of amebic colitis and amebic liver abscess. Many insights into the innate and acquired immune responses to infection with E. histolytica have been made in recent years. These findings have provided a foundation for producing a vaccine that could help to prevent the initial establishment of infection in the intestinal wall. The galactose and N-acetyl-D-galactosamine-specific lectin on the surface of the ameba is an immunodominant molecule that is highly conserved and has an integral role in the stimulation of these immune responses. The structure of the lectin has been defined, and the heavy subunit with its cysteine-rich region has been demonstrated in animal models to have some efficacy as a possible vaccine agent for prevention of amebic infection. Finding an ideal animal model of amebic intestinal infection has been difficult, but the C3H mouse and severe combined immunodeficient mouse-human intestinal xenograft models have both provided valuable insights into the first line of immune defense at the mucosal wall of the colon. Providing safe food and water to all people in the developing world is a formidable task that is not achievable in the foreseeable future. However, a vaccine for amebiasis could make a significant impact on the morbidity and mortality from the disease. Many components of the ameba are immunogenic and may serve as targets for a future vaccine, including the galactose and N-acetyl-D-galactosamine lectin, the serine-rich E. histolytica protein, cysteine proteinases, lipophosphoglycans, amebapores and the 29-kDa protein.

Matrix protein 2 vaccination and protection against influenza viruses, including subtype H5N1

Vaccination of mice with influenza matrix protein 2 induced cross-reactive antibody responses.

Changes in influenza viruses require regular reformulation of strain-specific influenza vaccines. Vaccines based on conserved antigens provide broader protection. Influenza matrix protein 2 (M2) is highly conserved across influenza A subtypes. To evaluate its efficacy as a vaccine candidate, we vaccinated mice with M2 peptide of a widely shared consensus sequence. This vaccination induced antibodies that cross-reacted with divergent M2 peptide from an H5N1 subtype. A DNA vaccine expressing full-length consensus-sequence M2 (M2-DNA) induced M2-specific antibody responses and protected against challenge with lethal influenza. Mice primed with M2-DNA and then boosted with recombinant adenovirus expressing M2 (M2-Ad) had enhanced antibody responses that cross-reacted with human and avian M2 sequences and induced T-cell responses. This M2 prime-boost vaccination conferred broad protection against challenge with lethal influenza A, including an H5N1 strain. Vaccination with M2, with key sequences represented, may provide broad protection against influenza A.

Comparative Membrane Channel Size and Activity of Botulinum Neurotoxins A and E

In an effort to compare the molecular basis of differential toxic activity of botulinum neurotoxin A (BoNT/A) and BoNT/E, we have analyzed their membrane channel activity by measuring calcein release from liposomes. Both BoNT/A and /E showed a same level of membrane channel activity that was specifically blocked by IgG specific to the neurotoxins. With the use of fluorescein-labeled dextran, we determined that the size of the channel is at least 24.2 A which is appropriate for the translocation of a protein of 50 kDa (the light chain of BoNT). These findings would suggest that the difference in the toxicity level of the two BoNT serotypes might reflect differences in either endopeptidase activity or their binding to receptor(s).

Autoimmune Channelopathies and Related Neurological Disorders

Ion channels are crucial elements in neuronal signaling and synaptic transmission, and defects in their function are known to underlie rare genetic disorders, including some forms of epilepsy. A second class of channelopathies, characterized by autoantibodies against ligand- and voltage-gated ion channels, cause a variety of defects in peripheral neuromuscular and ganglionic transmission. There is also emerging evidence for autoantibody-mediated mechanisms in subgroups of patients with central nervous system disorders, particularly those involving defects in cognition or sleep and often associated with epilepsy. In all autoimmune channelopathies, the relationship between autoantibody specificity and clinical phenotype is complex. But with this new information, autoimmune channelopathies are detected and treated with increasing success, and future research promises new insights into the mechanisms of dysfunction at neuronal synapses and the determinants of clinical phenotype.

The uncoupling protein 2 modulates the cytokine balance in innate immunity

The uncoupling protein 2 (UCP2) is located in the inner mitochondrial membrane and downregulates the production of reactive oxygen species (ROS). Recent data suggested a role for UCP2 in the immune response. We analyzed further this hypothesis during acute Listeria monocytogenes infection in mice. Death of infected Ucp2(-/-) mice was delayed in comparison with Ucp2(+/+), suggesting a role of UCP2 in the early step of the immune response. In vitro, the higher resistance of Ucp2(-/-) mice was not associated with a better control of bacterial growth by macrophages. In vivo, a significant increase of recruited phagocytes was observed in the spleen of Ucp2(-/-) mice. This was associated with a higher level of ROS in the spleen. Upregulation of pro-inflammatory cytokines IFNgamma, IL6, and IL1beta and of the chemokine MCP1 was observed in Ucp2(-/-) mice 4 days after infection, preceded by a decrease of the anti-inflammatory cytokine IL10 production. Present data highlight that, in an acute model of infection, UCP2 modulates innate immunity, via the modulation of ROS production, cytokine and chemokine production and consequently phagocyte recruitment.

[Antireceptor and antichannel autoantibodies]

This review of literature concerns the different autoantibodies directed against membrane receptors and ion channels. The target antigens, the associated pathologies, the pathogenesis and the methods of detection of these autoantibodies will be addressed. Some of these autoantibodies are thought to be closely related to the autoimmune disease whereas for some others their pathogenesis role is still unclear. Overall, the roles of antibodies are different between diseases, but the presence of such autoantibodies support the basis of intervening immunotherapy, antibody titers predicted the activity of the diseases and some of them are very specific and become the useful markers for the diagnosis. Some autoantibodies are detected routinely as the antiacetylcholine receptor, voltage-gated potassium and calcium channels autoantibodies whereas most of them are detected very rarely and only by specialized laboratories. This review will be divided in three parts with the following classification: the first group of autoantibodies directed against membrane receptors included receptors with an enzymatic activity (mostly tyrosine kinase) with one transmembrane domain, receptors associated to G protein with seven transmembrane domains, ion channels and receptors associated to the membrane by the glycosyl phosphatidyl inositol and the second group of intracellular receptor autoantibodies directed to the estrogens, androgens, lamin and kinesin receptors.

[Antireceptor and antichannel autoantibodies]

This review of literature concerns the different autoantibodies directed against membrane receptors and ion channels. The target antigens, the associated pathologies, the pathogenesis and the methods of detection of these autoantibodies will be addressed. Some of these autoantibodies are thought to be closely related to the auto-immune disease whereas for some others their pathogenesis role is still unclear. Overall, the roles of antibodies are different between diseases, but the presence of such autoantibodies support the basis of intervening immunotherapy, antibody titers predicted the activity of the diseases and some of them are very specific and become the useful markers for the diagnosis. Some autoantibodies are detected routinely as the antiacetylcholine receptor, voltage-gated potassium and calcium channels autoantibodies whereas most of them are detected very rarely and only by specialized laboratories. This review will be divided in three parts with the following classification: the first group of autoantibodies directed against membrane receptors included receptors with an enzymatic activity (mostly tyrosine kinase) with one transmembrane domain, receptors associated to G protein with seven transmembrane domains, ion channels and receptors associated to the membrane by the glycosylphosphatidylinositol and the second group of intracellular receptor autoantibodies directed to the estrogens, androgens, lamin and kinesin receptors.

[Antireceptor and antichannel autoantibodies]

This review of literature concerns the different autoantibodies directed against membrane receptors and ion channels. The target antigens, the associated pathologies, the pathogenesis and the methods of detection of these autoantibodies will be addressed. Some of these autoantibodies are thought to be closely related to the autoimmune disease whereas for some others their pathogenesis role is still unclear. Overall, the roles of antibodies are different between diseases, but the presence of such autoantibodies support the basis of intervening immunotherapy, antibody titers predicted the activity of the diseases and some of them are very specific and become the useful markers for the diagnosis. Some autoantibodies are detected routinely as the antiacetylcholine receptor, voltage-gated potassium and calcium channels autoantibodies whereas most of them are detected very rarely and only by specialized laboratories. This review will be divided in three parts with the following classification: the first group of autoantibodies directed against membrane receptors included receptors with an enzymatic activity (mostly tyrosine kinase) with one transmembrane domain, receptors associated to G protein with seven transmembrane domains, ion channels and receptors associated to the membrane by the glycosyl phosphatidyl inositol and the second group of intracellular receptor autoantibodies directed to the estrogens, androgens, lamin and kinesin receptors.

[Production of miniantibodies to Agrobacterium tumefaciens VirE2 virulence protein by the method of phage display]

The scFv miniantibodies to the recombinant protein VirE2 from Agrobacterium tumefaciens were obtained by the method of phage display. The miniantibodies were purified and tested using timmunodot method for binding to a recombinant protein from Escherichia coli and to the native protein VirE2 from A. tumefaciens. The functional activity of the miniantibodies was comparable to the activity of mouse polyclonal antibodies against the VirE2 protein.

Autoimmune channelopathies

Autoimmune disorders of the neuromuscular junction remain a paradigm for our understanding of autoimmunity. Since the role of autoantibodies to acetylcholine receptors in the pathogenesis of myasthenia gravis was first recognized in the 1970s, a range of antibody-mediated disorders of the neuromuscular junction have been described, each associated with an autoantibody to a specific ligand-gated receptor, voltage-gated ion channel or related protein. In addition, antibodies to a ganglionic form of acetylcholine receptor have been detected in autoimmune forms of autonomic neuropathy. In the past few years, a role for antibodies in disorders of the CNS has begun to emerge, challenging our previous concepts regarding the blood-brain barrier and the role of the humoral immune system in CNS pathology. Although it has not yet been definitively shown that these CNS conditions are antibody-mediated, the detection of the specific antibody supports a trial of immunosuppressive therapy to which many patients appear to respond. In this article, we review the roles of antibodies to receptors and ion channels in the peripheral and central nervous systems, concentrating on the recently defined autonomic and CNS conditions and on the role of antibody measurement in diagnosis and management.

Immunopharmacology--antibodies for specific modulation of proteins involved in neuronal function

The application of antibodies to living neurones has the potential to modulate function of specific proteins by virtue of their high specificity. This specificity has proven effective in determining the involvement of many proteins in neuronal function where specific agonists and antagonists do not exist, e.g. ion channel subunits. We discuss studies where antibodies modulate functions of voltage gated sodium, voltage gated potassium, voltage gated calcium hyperpolarisation activated cyclic nucleotide (HCN gated) and transient receptor potential (TRP) channels. Ligand gated channels studied in this way include nicotinic acetylcholine receptors, purinoceptors and GABA receptors. Antibodies have also helped reveal the involvement of different intracellular proteins in neuronal functions including G-proteins as well as other proteins involved in trafficking, phosphoinositide signalling and neurotransmitter release. Some suggestions for control experiments are made to help validate the method. We conclude that antibodies can be extremely valuable in determining the functions of specific proteins in living neurones in neuroscience research.

Expression and functional evaluation of transient receptor potential channel 4 in bovine corneal endothelial cells

We previously found that activation of purinergic receptors mobilizes Ca2+ and enhances bicarbonate transport in bovine corneal endothelial cells (BCEC). Since transient receptor potential channel 4 (TRPC) has been reported to be a candidate for capacitative calcium entry (CCE) and receptor operated calcium entry (ROC), we examined the expression of TRPC4 and evaluated the potential involvement of TRPC4 in CCE or ROC in BCEC. The C-terminus of TRPC4 was fused into the glutathione S-transferase (GST) expression vector. The fusion protein GST-TRPC4c was induced in bacteria and purified by affinity chromatography. An antibody was raised in rabbit by using the purified GST-TRPC4c antigen. In Western blotting, the TRPC4 antibody recognized the fusion protein while the pre-immune IgG did not. The TRPC4 antibody recognized a band at around 80 kD for membrane proteins from both the fresh and cultured BCEC. The pre-immune IgG could not detect bands at the same size. Incubation with the TRPC4c antigen abolished the 80 kD band. Immunofluorescence using the TRPC4 antibody stained both fresh and cultured BCEC, while pre-immune IgG did not. RNAi knocked down the expression of TRPC4 in cultured BCEC. Ca2+ entry induced by the purinergic receptor agonist ATP, was increased in TRPC4-siRNA transfected cells compared with the scrambled siRNA control, while Ca2+ entry induced by store depletion through blocking the endoplasmic reticulum Ca2+ pump, did not differ between the siRNA and scrambled siRNA-treated cells. Taken together, these results show that TRPC4 protein is expressed in the bovine corneal endothelial cells and may be a negative regulator in ROC stimulated by purinergic activation, but not by store depletion itself.

Immunological role of neuronal receptor vanilloid receptor 1 expressed on dendritic cells

Capsaicin (CP), the pungent component of chili pepper, acts on sensory neurons to convey the sensation of pain. The CP receptor, vanilloid receptor 1 (VR1), has been shown to be highly expressed by nociceptive neurons in dorsal root and trigeminal ganglia. We demonstrate here that the dendritic cell (DC), a key cell type of the vertebrate immune system, expresses VR1. Engagement of VR1 on immature DCs such as by treatment with CP leads to maturation of DCs as measured by up-regulation of antigen-presenting and costimulatory molecules. This effect is present in DCs of VR1+/+ but not VR1-/- mice. In VR1+/+ mice, this effect is inhibited by the VR1 antagonist capsazepine. Further, intradermal administration of CP leads to migration of DCs to the draining lymph nodes in VR1+/+ but not VR1-/- mice. These data demonstrate a powerful influence of a neuroactive ligand on a central aspect of immune function and a commonality of mechanistic pathways between neural and immune functions.

Isolation, purification, and identification of the virulence protein VirE2 from Agrobacterium tumefaciens

Bacteria of the genus Agrobacterium can transfer a portion of their Ti plasmid (T-DNA) in complex with the VirE2 and VirD2 proteins into the plant-cell nucleus and cause it to be integrated in the host-cell chromosomes. The mechanism of T-DNA transfer across the plant-cell membrane and cytoplasm is unknown. The aim of this study was to isolate the virulence protein VirE2 in order to explore its role in T-DNA transfer across the eukaryotic-cell membrane and cytoplasm. To obtain VirE2, we cloned the virE2 gene into plasmid pQE31 in Escherichia coli cells. VirE2 protein was isolated from E. coli XL-1 blue cells containing a recombinant plasmid, pQE31-virE2. The cells were ultrasonically disrupted, and the protein containing six histidine residues at the N-terminal end was isolated by affinity chromatography on Ni-NTA agarose. The purified preparation was tested by immunodot, by using polyclonal rabbit antibodies and miniantibodies produced toward VirE2. The capacity of the recombinant protein VirE2 for interacting with single-stranded DNA was tested by the formation of complexes, recorded by agarose-gel electrophoresis. In summary, A. tumefaciens virulence protein VirE2, capable of forming a complex with single-stranded T-DNA during transfer into the plant cell, was isolated, purified, and partially characterized. Anti-VirE2 miniantibodies were obtained, and direct labeling of VirE2 with colloidal gold was done for the first time.

[Isolation, purification, and identification of virulence protein VirE2 from Agrobacterium tumefaciens]

Bacteria of the genus Agrobacterium are capable of transferring a fragment of their Ti-plasmid, T-DNA, in a complex with the proteins VirE2 and VirD2, into the nuclei of plant cells and incorporating it into the chromosome of the host. The mechanisms of T-DNA transportation through membrane and cytoplasm of the plant cell are unknown. The aim of this work was isolation of virulence protein VirE2 for studying its role in T-DNA transportation through the membrane and cytoplasm of eukaryotic cells. For VirE2 accumulation, virE2 gene was cloned into plasmid pQE31. VirE2 was isolated from the cells of E. coli strain XL1-blue, containing the recombinant plasmid pQE31-virE2. The cells were disrupted ultrasonically, and the protein with six histidine residues at the N-end was isolated by means of affinity chromatography on a Ni-NTA-superose column. The purified protein was tested by the immunodot method using polyclonal rabbit antibodies and anti-VirE2 miniantibodies. The ability of the recombinant protein VirE2 to bind to single-stranded DNA was judged from the formation of complexes detected by electrophoresis in agarose gel. Thus, we isolated, purified, and partially characterized the Agrobacterium tumefaciens virulence protein VirE2 which is capable of binding to single-stranded T-DNA upon transfer to the plant cell.

TRPA1 is a candidate for the mechanosensitive transduction channel of vertebrate hair cells

Mechanical deflection of the sensory hair bundles of receptor cells in the inner ear causes ion channels located at the tips of the bundle to open, thereby initiating the perception of sound. Although some protein constituents of the transduction apparatus are known, the mechanically gated transduction channels have not been identified in higher vertebrates. Here, we investigate TRP (transient receptor potential) ion channels as candidates and find one, TRPA1 (also known as ANKTM1), that meets criteria for the transduction channel. The appearance of TRPA1 messenger RNA expression in hair cell epithelia coincides developmentally with the onset of mechanosensitivity. Antibodies to TRPA1 label hair bundles, especially at their tips, and tip labelling disappears when the transduction apparatus is chemically disrupted. Inhibition of TRPA1 protein expression in zebrafish and mouse inner ears inhibits receptor cell function, as assessed with electrical recording and with accumulation of a channel-permeant fluorescent dye. TRPA1 is probably a component of the transduction channel itself.

Novel aspects of signaling and ion-homeostasis regulation in immunocytes. The TRPM ion channels and their potential role in modulating the immune response

In just a few years, the discovery and subsequent characterization of several members of the TRPM family of cation channels have provided us with surprising new insights into unknown aspects of cellular ion-homeostasis regulation. This includes reports about ADP-ribose functioning as a novel intracellular second messenger and gating molecule of the Ca(2+)-permeable TRPM2 channel, studies demonstrating the central role of mouse TRPM5 in taste signaling, as well as the unexpected involvement of TRPM6 and TRPM7 in regulating Mg(2+)-homeostasis, or the cool properties of TRPM8 acting as a cold and menthol sensor in sensory neurons. At least four of the eight known TRPM proteins have been shown to be present in the immune context: TRPM1 (melastatin), TRPM2, TRPM4 and TRPM7. Although we currently lack animal models allowing a detailed assessment of the potential involvement of TRPM family members in modulating the immune response, the powerful combination of molecular and cellular biology, biochemistry, and electrophysiology have provided the first clues as to how these molecules could contribute to immunity.

Increased expression of transient receptor potential vanilloid-1 in airway nerves of chronic cough

Transient receptor potential vanniloid-1 (TRPV-1) mediates the cough response induced by the pepper extract capsaicin and is expressed in sensory nerves that innervate the airway wall. We determined the expression of TRPV-1 in the airways of patients with chronic persistent cough of diverse causes and with an enhanced capsaicin cough response. We obtained airway mucosal biopsies by fiberoptic bronchoscopy in 29 patients with chronic cough and 16 healthy volunteers without a cough. Immunostaining for nerve profiles with anti-protein gene product (PGP)-9.5 antibody showed no increase in nerve profiles in the airway epithelium of patients with chronic cough; however, with an anti-TRPV-1 antibody, there was a fivefold increase of TRPV-1 staining nerve profiles (p < 0.001). There was a significant correlation between capsaicin tussive response and the number of TRPV-1-positive nerves within the patients with cough. Our findings indicate that TRPV-1 receptors may contribute to an enhanced cough reflex and the cough response in chronic persistent cough of diverse causes.

Hg2+ and small-sized polyethylene glycols have inverse effects on membrane permeability, while both impair neutrophil cell motility

Toxic effects after exposure to mercury are well documented in human. Little is, however, known about how Hg(2+) affect host defense in general and neutrophil functions in particular. We show here that exposure of human neutrophils to HgCl(2) dose-dependently impairs chemoattractant-stimulated motility. Long-term exposure (5-10 min) to Hg(2+) yields a rapid influx of extracellular Ca(2+) followed by leakage of cytosolic fluorophores, as assessed using fura-2 and ratio imaging microscopy. The inhibition on motility was partly reversible, since pre-treated neutrophils placed in an Hg(2+)-free environment displayed higher migration rates. The Hg(2+)-induced fluxes were prevented by addition of small-sized polyethylene glycols (PEG 200-400), which also dose-dependently inhibited neutrophil transmigration. Localized, minute micropipette additions of Hg(2+) or PEG caused retraction of the leading edge and redirection of cell migration. Since Hg(2+) increases and PEGs decrease membrane permeability in a partially competitive manner, we suggest that the known aquaporin-inhibitor Hg(2+) alters membrane permeability by affecting the bidirectional flux through the leukocyte aquaporin-9 (AQP9) while small-sized PEGs yield decreased membrane permeability by becoming trapped in the promiscuous channel. The local additions of Hg(2+) or PEG probably force other cell regions to take over from those with blocked AQPs. Hence, the cells turn direction of motility away from the micromanipulator needle.

Epitope Tagging of the Yeast K+ Carrier Trk2p Demonstrates Folding That Is Consistent with a Channel-like Structure

TRK family proteins, which mediate the concentrative uptake of potassium by plant cells, fungi, and bacteria, resemble primitive potassium channels in sequence and have recently been proposed actually to fold like potassium channels in a 4-MPM motif (Durell, S. R., and Guy, H. R. (1999) Biophys. J. 77, 789 - 807), instead of like conventional substrate porters in the 12-TM motif (Gaber, R. F., Styles, C. A., and Fink, G. R. (1988) Mol. Cell. Biol. 8, 2848-2859). The known fungal members of this family possess a very long hydrophilic loop, positioned intracellularly in the K(+)-channel model and extracellularly in the substrate porter model. This and two shorter hydrophilic segments have been tested as topological markers for the true folding pattern of TRK proteins using Saccharomyces cerevisiae Trk2p. Hemagglutinin epitope tags were inserted into all three segments, and the enhanced green fluorescent protein (EGFP) was fused to the C terminus of Trk2p. The gene constructs were expressed from a high copy plasmid, and sidedness of the tags was determined by native fluorescence (EGFP), indirect immunofluorescence, and immunoelectron microscopy. Both the long-loop tag and the C-terminal EGFP fusion allowed abundant protein to reach the plasma membrane and support normal yeast growth. In all determinations, the long-loop tag was localized to the inner surface of the yeast cell plasma membrane, thus strongly supporting the channel-like folding model. Additional observations showed (i). membrane-associated Trk2p to lie in proteolipid rafts; (ii). significant tagged protein, expressed from the plasmid, to be sequestered in cytoplasmic vesicular-tubular clusters; and (iii). suppression of such clusters by yeast growth in 5-10% glycerol. This chaperone-like effect may assist other membrane proteins (overexpressed or heterologously expressed) to function within the yeast plasma membrane.

Malate and malate-channel antibodies inhibit electrogenic and ATP-dependent citrate transport across the tonoplast of citrus juice cells

Citrus juice cells accumulate high levels of citric acid in their vacuoles when compared to other organic ions including malate. Uptake of citrate into tonoplast vesicles from Citrus juice cells was investigated in the presence of malate, and after incubation with antibodies raised against the vacuolar malate-specific channel of Kalanchoë diagremontiana leaves. Antibodies against the vacuolar malate channel immunoreacted with a protein of similar size in tonoplast extracts from three Citrus varieties differing in citric acid content. Malate channel antibodies inhibited both delta MicroH(+)-dependent and delta MicroH(+)-independent ATP-dependent citrate transport, indicating common domains in both transport systems and to the malate-specific channel of Kalanchoë diagremontiana leaves. Malate strongly inhibited electrogenic citrate transport, whereas ATP-dependent citrate uptake was less affected. Kinetic analysis of citrate transport in the presence of malate confirmed the existence of two citrate transport mechanisms and indicated that both citrate and malate share a common transport channel across the tonoplast of Citrus juice cells.

Identification of an HLA-A*0201-restricted T-cell epitope derived from the prostate cancer-associated protein trp-p8

BACKGROUND

New concepts for the immunotherapy of prostate carcinoma (PCa) largely depend on the identification of suitable target antigens that are present in a high percentage of prostate tumors. Their expression in normal tissues should be restricted to the prostate and they should be immunogenic in vivo. The number of antigens displaying these properties is still limited. Here, we identify for the first time an immunogenic peptide derived from the prostate-specific protein transient receptor potential-p8 (trp-p8) that is recognized by cytotoxic T lymphocytes (CTLs) from PCa patients.

METHODS

To determine the abundance of trp-p8 in prostate tumors, the expression level of trp-p8 mRNA was quantitatively analyzed in a panel of prostate cancer tissues. Trp-p8-derived human leukocyte antigen (HLA)-A*0201-restricted peptides were selected and tested for the in vitro activation of CTLs when loaded on autologous dendritic cells (DCs).

RESULTS

Trp-p8 mRNA was found to be expressed in all prostate tumors and in the corresponding normal prostate tissue. Of five selected trp-p8-derived peptides, only peptide GLMKYIGEV was shown to activate specific CTLs, which effectively lysed PCa cells confirming the endogenous generation and presentation of this peptide by tumor cells.

CONCLUSIONS

Our results suggest this antigen as a suitable target for the T-cell-based immunotherapy of PCa.

HCN channels are expressed differentially in retinal bipolar cells and concentrated at synaptic terminals

Hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels codetermine the integrative behaviour of neurons and shape their response to synaptic stimulation. We used immunohistochemistry and patch-clamp recording to study the composition and distribution of HCN channels in the rat retina. All four HCN channel isoforms (HCN1-4) are expressed differentially in the retina. In particular, different classes of bipolar cells have a different inventory of HCN channels. We found no evidence for the formation of heterooligomeric HCN channels. HCN channels are densely clustered at synaptic terminals of bipolar cells and photoreceptors. This suggests that HCN channels are involved in the control of transmitter release.

Autoantibodies to ion channels at the neuromuscular junction

Autoantibodies directed against voltage- or ligand-gated ion channels and their associated proteins at the neuromuscular junction give rise to a family of neurological autoimmune diseases. Antibodies to acetylcholine receptors or muscle-specific kinase present on the postsynaptic muscle membrane are associated with different forms of myasthenia gravis (MG). Antibodies to the presynaptic voltage-gated potassium and calcium channels are responsible for acquired neuromyotonia and Lambert-Eaton myasthenic syndrome (LEMS), respectively. The patients respond to immunotherapies and their plasma can transfer defects in neuromuscular transmission to mice, indicating that these are antibody-mediated conditions. In a small proportion of cases, ion channel antibodies have also been implicated in neurological dysfunction in the central nervous system. In these conditions, a proportion of the patients have an underlying tumour, thymoma in both MG and neuromyotonia and small cell lung carcinoma in LEMS, emphasising the putative role of autoimmunity to tumour antigens as a cause of neurological disease.

Ion channel and striational antibodies define a continuum of autoimmune neuromuscular hyperexcitability

Neuromuscular hyperexcitability is a characteristic of Isaacs' syndrome. Autoantibodies specific for voltage-gated potassium channels (VGKC) or ganglionic nicotinic acetylcholine receptors (AChR) are markers of this disorder. To determine the frequency of these ion channel antibodies and of related neuron- and muscle-specific antibodies in patients with acquired neuromuscular hyperexcitability, we tested serum specimens from 77 affected patients (35 neuromyotonia, 32 cramp-fasciculation syndrome, 5 rippling muscle syndrome, and 5 focal neuromuscular hyperexcitability) and 85 control subjects. Among study patients, 14% had coexisting myasthenia gravis, and 16% had an associated neoplasm. We found that 35% had VGKC antibodies, 12% ganglionic AChR antibodies, 16% muscle AChR antibodies, and 10% striational antibodies. Overall, 55% had serological evidence of neurological autoimmunity compared to 2% of control subjects. Patients with neuromyotonia were more frequently seropositive (71%) than patients with cramp-fasciculation syndrome (31%). We conclude that acquired neuromuscular hyperexcitability consists of a continuum of clinical disorders with a common autoimmune pathogenesis.

Chemokine receptor CXCR2 regulates the functional properties of AMPA-type glutamate receptor GluR1 in HEK cells

Experiments were conducted in both HEK cells and cerebellar neurons to investigate whether CXC chemokine receptor 2 (CXCR2) is functionally coupled to GluR1. The co-expression of CXCR2 with GluR1 in HEK cells increased (i) the GluR1 "apparent" affinity for the transmitter; (ii) the GluR1 channel open probability; and (iii) GluR1 binding site cooperativity upon CXCR2 stimulation with CXC chemokine ligand 2 (CXCL2). The affinity of C-terminal-deleted GluR1 for glutamate (Glu) remained stable instead. Furthermore, CXCL2 increased the binding site cooperativity of AMPA receptors in rat cerebellar granule cells; and the amplitude of spontaneous excitatory postsynaptic current (sEPSCs) in Purkinje neurons (PNs). Our findings indicate that the coupling of CXCR2 with GluR1 may modulate glutamatergic synaptic transmission.

The continuing importance of thyroid scintigraphy in the era of high-resolution ultrasound

At the molecular level, the uptake of radioiodine and pertechnetate is proportional to the expression of the thyroidal sodium/iodine symporter (NIS). Qualitative and quantitative scintigraphic evaluation of the thyroid is performed with a gamma camera fitted with an on-line computer system and enables determination of the iodine uptake or the technetium uptake (TCTU) as an iodine clearance equivalent. Despite new molecular genetic insights into congenital hypothyroidism, the iodine-123 or pertechnetate scan remains the most accurate test for the detection of ectopic thyroid tissue. Following the identification of specific mutations of the genes coding for the NIS, thyroid peroxidase and pendrin, the discharge test has lost its role in establishing the diagnosis of inherited dyshormonogenesis, but it is still of value in the assessment of defect severity. In PDS mutations the test can be used to establish the diagnosis of syndromic disease. Quantitative pertechnetate scintigraphy is the most sensitive and specific technique for the diagnosis and quantification of thyroid autonomy. The method has proved to be valuable in risk stratification of spontaneous or iodine-induced hyperthyroidism, in the estimation of the target volume prior to radioiodine therapy and in the evaluation of therapeutic success after definitive treatment. In iodine deficiency areas the thyroid scan remains indispensable for the functional characterisation of a thyroid nodule and is still a first-line diagnostic procedure in cases of suspected thyroid malignancy. This is especially of importance in patients with Graves' disease, among whom a relatively high prevalence of cancer has been found in cold thyroid nodules. While determination of the TCTU is without any value in the differentiation between autoimmune thyroiditis and Graves' disease in most cases, it is of substantial importance in the differentiation between hyperthyroid autoimmune thyroiditis and Graves' disease.

[Channelopathy]

Recently, a variety of ion channel defects have been identified as the biological basis of certain familial epilepsies, paroxysmal movement disorders, myopathies and some degenerative disorders of central nervous system. Ion channel defects were mainly caused by genetic and autoimmune mechanisms. Here, we reviewed several channelopathies including spinocerebellar ataxia type 6, familial hemiplegic migraine, episodic ataxia type 2, familial hypokalemic periodic paralysis, congenital myotonia, malignant hyperthermia, epilepsy, Gitelman syndrome and Lambert-Eaton syndrome.

Molecular properties and physiological roles of ion channels in the immune system

The discovery of a diverse and unique set of ion channels in T lymphocytes has led to a rapidly growing body of knowledge about their functional roles in the immune system. Here we review the biophysical and molecular characterization of K+, Ca2+, and Cl- channels in T lymphocytes. Potent and specific blockers, especially of K+ channels, have provided molecular tools to elucidate the involvement of voltage- and calcium-activated potassium channels in T-cell activation and cell-volume regulation. Their unique and differential expression makes lymphocyte K+ channels excellent pharmaceutical targets for modulating immune system function. This review surveys recent progress at the biophysical, molecular, and functional roles of the ion channels found in T lymphocytes.

Structural and functional diversity of blood group antigens

Biochemical and molecular genetic studies have revealed that blood group antigens are present on cell surface molecules of wide structural diversity, including carbohydrate epitopes on glycoproteins and/or glycolipids, and peptide antigens on proteins inserted within the membrane via single or multi-pass transmembrane domains, or via glycosylphosphatidylinositol linkages. These studies have also shown that some blood group antigens are carried by complexes consisting of several membrane components which may be lacking or severely deficient in rare blood group 'null' phenotypes. In addition, although all blood group antigens are serologically detectable on red blood cells (RBCs), most of them are also expressed in non-erythroid tissues, raising further questions on their physiological function under normal and pathological conditions. In addition to their structural diversity, blood group antigens also possess wide functional diversity, and can be schematically subdivided into five classes: i) transporters and channels; ii) receptors for ligands, viruses, bacteria and parasites; iii) adhesion molecules; iv) enzymes; and v) structural proteins. The purpose of this review is to summarize recent findings on these molecules, and in particular to illustrate the existing structure-function relationships.

Regulation of P2X(7) nucleotide receptor function in human monocytes by extracellular ions and receptor density

P2X receptors function as ATP-gated cation channels. The P2X(7) receptor subtype is distinguished from other P2X family members by a very low affinity for extracellular ATP (millimolar EC50) and its ability to trigger induction of nonselective pores on repeated or prolonged stimulation. Previous studies have indicated that certain P2X(7) receptor-positive cell types, such as human blood monocytes and murine thymocytes, lack this pore-forming response. In the present study we compared pore formation in response to P2X(7) receptor activation in human blood monocytes with that in macrophages derived from these monocytes by in vitro tissue culture. ATP induced nonselective pores in macrophages but not in freshly isolated monocytes when both cell types were identically stimulated in standard NaCl-based salines. However, ion substitution studies revealed that replacement of extracellular Na+ and Cl- with K+ and nonhalide anions strongly facilitated ATP-dependent pore formation in monocytes. These ionic conditions also resulted in increased agonist affinity, such that 30-100 microM ATP was sufficient for activation of nonselective pores by P2X(7) receptors. Comparison of P2X(7) receptor expression in blood monocytes with that in macrophages indicated no differences in steady-state receptor mRNA levels but significant increases (up to 10-fold) in the amount of immunoreactive P2X(7) receptor protein at the cell surface of macrophages. Thus ability of ATP to activate nonselective pores in cells that natively express P2X(7) receptors can be modulated by receptor subunit density at the cell surface and ambient levels of extracellular Na+ and Cl-. These mechanisms may prevent adventitious P2X(7) receptor activation in monocytes until these proinflammatory leukocytes migrate to extravascular sites of tissue damage.

Localization of aquaporin-7 in rat and mouse kidney using RT-PCR, immunoblotting, and immunocytochemistry

To establish the segmental, cellular, and subcellular localization of AQP7 in rat and mouse kidney, we used RT-PCR, immunocytochemical, and immunoblotting approaches. RT-PCR of rat and mouse kidney zones revealed AQP7 mRNA in cortex and outer stripe of the outer medulla. RT-PCR on microdissected nephron segments revealed AQP7 mRNA in proximal convoluted and straight tubules. Immunoblotting using peptide-derived rabbit antibodies to either rat or mouse AQP7 revealed a 28-kDa band in kidney and testes from rat and mouse, respectively. Immunocytochemistry revealed strong AQP7 labeling of segment 3 proximal tubules and weaker labeling of proximal convoluted tubules in both rat and mouse kidneys. The labeling was almost exclusively confined to the brush border with no basolateral labeling. No labeling was observed of thin descending limbs or collecting duct. Immunolabeling controls were negative. The presence of AQP7 in the proximal tubule brush border indicates a role of AQP7 in proximal tubule water reabsorption.

Localization of the olfactory cyclic nucleotide-gated channel subunit 1 in normal, embryonic and regenerating olfactory epithelium

The spatial and temporal expression of subunit 1 of the olfactory cyclic nucleotide-gated channel was investigated using affinity-purified anti-fusion protein antibodies. Immunoreactivity was most prominent in the ciliary layer of the olfactory epithelium, but high protein expression was also seen along the entire length of olfactory receptor neuronal axons to the level of the glomeruli. Electron microscopy showed that the long, thin distal compartments of olfactory cilia labeled more prominently than their thicker proximal segments. This was true as soon as these distal parts began to develop. Using light microscopy, developmental expression of olfactory cyclic nucleotide-gated channel subunit 1 could be detected in discrete populations of olfactory receptor neurons by embryonic day 14. Other signaling molecules are expressed either later (Golf) or only at the level of the epithelial surface and not in axons (adenylyl cyclase type III). Following unilateral lesions of the olfactory bulb, olfactory cyclic nucleotide-gated channel subunit 1 immunoreactivity was present early and throughout developing olfactory receptor neurons; adenylyl cyclase type III immunoreactivity, in contrast, was detectable only later, and again present only in the cilial layer. These results support the hypothesis that this subunit of the olfactory cyclic nucleotide-gated channel may be involved in olfactory axon guidance, in addition to its well-described role in olfactory signal transduction.

Identification of autoantibodies associated with rippling muscles and myasthenia gravis that recognize skeletal muscle proteins: possible relationship of antigens and stretch-activated ion channels

The role of mechanosensitive calcium channels in skeletal muscle physiology is not understood. This study takes advantage of an autoimmune neuromuscular disorder (myasthenia gravis associated with rippling muscles) to identify components in the skeletal muscle myocyte that may play a role in mechanosensitive calcium channel activity. Rippling muscles are characterized by stretch or percussion activated wave-like muscle contractions that do not require motor unit action potentials for propagation. Autoantibodies from the sera of patients with autoimmune rippling muscles (associated with myasthenia gravis) are directed against high molecular weight muscle proteins. Some of these proteins are uniquely recognized by antisera from patients with autoimmune rippling muscles. This suggests these autoantigens are distinct from those normally associated with myasthenia gravis, and may play a role in the mechanosensitive activation of muscle contraction.