The action of Lambert-Eaton myasthenic syndrome immunoglobulin G on cloned human voltage-gated calcium channels

Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disease characterized by proximal muscle weakness, loss of tendon reflexes, and autonomic dysfunction. Muscle weakness usually starts in the upper legs and can progress to oculobulbar and in severe cases respiratory muscles. P/Q-type voltage-gated calcium channels (VGCCs) localized in the presynaptic motor nerve terminal and in the autonomic nervous system are targeted by antibodies in LEMS patients. These antibodies can be detected in about 90% of patients, and the presence of decrement and increment upon repetitive nerve stimulation is also a highly sensitive diagnostic test. Rapid diagnosis is important because of the association with SCLC in 50%-60% of patients, which stresses the need for vigorous tumor screening after diagnosis. Clinical parameters can predict tumor probability and guide frequency of tumor screening. Treatment of the tumor as well as symptomatic treatment and immunosuppression can effectively control symptoms in the majority of patients.

Presynaptic Paraneoplastic Disorders of the Neuromuscular Junction: An Update

The neuromuscular junction (NMJ) is the target of a variety of immune-mediated disorders, usually classified as presynaptic and postsynaptic, according to the site of the antigenic target and consequently of the neuromuscular transmission alteration. Although less common than the classical autoimmune postsynaptic myasthenia gravis, presynaptic disorders are important to recognize due to the frequent association with cancer. Lambert Eaton myasthenic syndrome is due to a presynaptic failure to release acetylcholine, caused by antibodies to the presynaptic voltage-gated calcium channels. Acquired neuromyotonia is a condition characterized by nerve hyperexcitability often due to the presence of antibodies against proteins associated with voltage-gated potassium channels. This review will focus on the recent developments in the autoimmune presynaptic disorders of the NMJ.

The role of the laboratory in the expanding field of neuroimmunology: Autoantibodies to neural targets

Accelerated identification of autoantibodies associated with previously idiopathic neurological disease has provided insights into disease mechanisms, enhanced understanding of neurological function, and opportunities for improved therapeutic interventions. The role of the laboratory in the expanding field of neuroimmunology is critical as specific autoantibody identification provides guidance to clinicians in diagnosis, prognosis, tumor search strategies, and therapeutic interventions. The number of specific autoantibodies identified continues to increase and newer testing strategies increase efficiencies in the laboratory and availability to clinicians. The need for broadly targeted efficient testing is underscored by the variability in clinical presentation and tumor associations attributable to a specific autoantibody, and conversely the various autoantibody specificities that can be the cause of a given clinical presentation. While many of the antineural antibodies were first recognized in the setting of neoplastic disease, idiopathic autoimmune neurological disease in the absence of underlying tumor is increasingly recognized. Appropriation of therapeutic modalities used to treat autoimmune disease to treat these autoantibody mediated neurological diseases has improved patient outcomes. Interaction between clinicians and laboratorians is critical to our understanding of these diseases and optimization of the clinical benefits of our increasing knowledge in neuroimmunology.

Long-term survival in paraneoplastic Lambert-Eaton myasthenic syndrome

Objective:

To establish whether improved tumor survival in patients with Lambert-Eaton myasthenic syndrome (LEMS) and small-cell lung cancer (SCLC) was due to known prognostic risk factors or an effect of LEMS independently, perhaps as a result of circulating factors.

Methods:

We undertook a prospective observational cohort study of patients with LEMS attending Nottingham University Hospitals, UK, or via the British Neurological Surveillance Unit. In parallel, patients with a new diagnosis of biopsy-proven SCLC were enrolled, examined for neurologic illness, and followed up until death or study end.

Results:

Between May 2005 and November 2014, we recruited 31 patients with LEMS and SCLC and 279 patients with SCLC without neurologic illness. Allowing for known SCLC survival prognostic factors of disease extent, age, sex, performance status, and sodium values, multivariate Cox regression analysis showed that the presence of LEMS with SCLC conferred a significant survival advantage independently of the other prognostic variables (hazard ratio 1.756, 95% confidence interval 1.137–2.709, p = 0.011).

Conclusions:

Improved SCLC tumor survival seen in patients with LEMS and SCLC may not be due solely to lead time bias, given that survival advantage remains after allowing for other prognostic factors and that the same degree of survival advantage is not seen in patients with paraneoplastic neurologic syndromes other than LEMS presenting before SCLC diagnosis.

Autoimmune synaptopathies

Autoantibodies targeting proteins at the neuromuscular junction are known to cause several distinct myasthenic syndromes. Recently, autoantibodies targeting neurotransmitter receptors and associated proteins have also emerged as a cause of severe, but potentially treatable, diseases of the CNS. Here, we review the clinical evidence as well as in vitro and in vivo experimental evidence that autoantibodies account for myasthenic syndromes and autoimmune disorders of the CNS by disrupting the functional or structural integrity of synapses. Studying neurological and psychiatric diseases of autoimmune origin may provide new insights into the cellular and circuit mechanisms underlying a broad range of CNS disorders.

Neurologic autoimmunity: mechanisms revealed by animal models

Over the last decade, neurologic autoimmunity has become a major consideration in the diagnosis and management of patients with many neurologic presentations. The nature of the associated antibodies and their targets has led to appreciation of the importance of the accessibility of the target antigen to antibodies, and a partial understanding of the different mechanisms that can follow antibody binding. This chapter will first describe the basic principles of autoimmune inflammation and tissue damage in the central and peripheral nervous system, and will then demonstrate what has been learnt about neurologic autoimmunity from circumstantial clinical evidence and from passive, active, and occasionally spontaneous or genetic animal models. It will cover neurologic autoimmune diseases ranging from disorders of neuromuscular transmission, peripheral and ganglionic neuropathy, to diseases of the central nervous system, where autoantibodies are either pathogenic and cause destruction or changes in function of their targets, where they are harmless bystanders of T-cell-mediated tissue damage, or are not involved at all. Finally, this chapter will summarize the relevance of current animal models for studying the different neurologic autoimmune diseases, and it will identify aspects where future animal models need to be improved to better reflect the disease reality experienced by affected patients, e.g., the chronicity or the relapsing/remitting nature of their disease.

Lambert-Eaton syndrome IgG inhibits transmitter release via P/Q Ca2+ channels

Objective:

To determine whether immunoglobulin G (IgG) from patients with Lambert-Eaton myasthenic syndrome (LEMS) decreases action potential–evoked synaptic vesicle exocytosis, and whether the effect is mediated by P/Q-type voltage-gated calcium channels (VGCCs).

Methods:

IgG was obtained from 4 patients with LEMS (3 males, 1 female), including 2 patients with lung malignancy. Antibodies against P/Q-type VGCCs were detected in all 4 patients, and against N-type VGCCs in 2. We incubated neuronal cultures with LEMS IgG and determined the size of the total recycling pool of synaptic vesicles and the rate of action potential–evoked exocytosis using fluorescence imaging of the amphiphilic dye SynaptoRed C1. Pooled IgG from healthy volunteers was used as a control. We repeated the experiments on synapses lacking P/Q-type calcium channels from a Cacna1a knockout mouse to determine whether these channels account for the pathogenic effect of LEMS IgG.

Results:

LEMS IgG had no effect on the total recycling pool size but significantly reduced the rate of action potential–evoked synaptic exocytosis in wild-type neurons when compared with neurons treated with control IgG. In contrast, LEMS IgG had no effect on the rate of synaptic vesicle exocytosis in neurons lacking P/Q-type channels.

Conclusions:

These data provide direct evidence that LEMS IgG inhibits neurotransmitter release by acting on P/Q-type VGCCs.

Neuronal autoantigens--pathogenesis, associated disorders and antibody testing

The discovery of disorders that are associated with antibodies to neuronal cell-surface proteins has led to a paradigm shift in our understanding of CNS autoimmunity. These disorders can occur in patients with or without cancer-often children or young adults who develop psychosis, catatonic or autistic features, memory problems, abnormal movements, or seizures that were previously considered idiopathic. The autoantigens in such cases have crucial roles in synaptic transmission, plasticity and peripheral nerve excitability. Patients can be comatose or encephalopathic for months and yet fully recover with supportive care and immunotherapy. By contrast, disorders in which the antibodies target intracellular antigens, and in which T-cell-mediated irreversible neuronal degeneration occurs, show a considerably poorer response to treatment. In this article, we review the various targets of neuronal antibodies, focusing predominantly on autoantigens located on the cell surface or synapses-namely, N-methyl-D-aspartate receptors, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, γ-aminobutyric acid receptors, leucine-rich glioma-inactivated protein 1, contactin-associated protein-like 2, and metabotropic glutamate receptors. We also provide an algorithm to identify and assess antibodies that bind to cell-surface and synaptic antigens.

Lambert-Eaton myasthenic syndrome: from clinical characteristics to therapeutic strategies

Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular autoimmune disease that has served as a model for autoimmunity and tumour immunology. In LEMS, the characteristic muscle weakness is thought to be caused by pathogenic autoantibodies directed against voltage-gated calcium channels (VGCC) present on the presynaptic nerve terminal. Half of patients with LEMS have an associated tumour, small-cell lung carcinoma (SCLC), which also expresses functional VGCC. Knowledge of this association led to the discovery of a wide range of paraneoplastic and non-tumour-related neurological disorders of the peripheral and central nervous systems. Detailed clinical studies have improved our diagnostic skills and knowledge of the pathophysiological mechanisms and association of LEMS with SCLC, and have helped with the development of a protocol for early tumour detection.

3,4-diaminopyridine for the treatment of Lambert-Eaton myasthenic syndrome

The Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease in which antibodies against voltage-gated calcium channels inhibit cholinergic neurotransmission. LEMS is clinically characterized by muscle weakness and autonomic dysfunction. 3,4-diaminopyridine (3,4-DAP) blocks potassium channels in nerve terminals, resulting in an increase in acetylcholine release. This article describes the four randomized placebo-controlled trials of 3,4-DAP in patients with LEMS. All trials demonstrated a significant effect on muscle strength and compound muscle action potential amplitude. Furthermore, the safety and tolerability of 3,4-DAP are reviewed. The side effects of 3,4-DAP are generally mild and most frequently consist of paresthesias, but epileptic seizures and arrhythmias have been described in patients using high doses. Given the efficacy and safety of 3,4-DAP in LEMS, this drug is the mainstay for symptomatic treatment of LEMS.

Mechanisms underlying autoimmune synaptic encephalitis leading to disorders of memory, behavior and cognition: insights from molecular, cellular and synaptic studies

Recently, several novel, potentially lethal and treatment-responsive syndromes that affect hippocampal and cortical function have been shown to be associated with auto-antibodies against synaptic antigens, notably glutamate or GABA-B receptors. Patients with these auto-antibodies, sometimes associated with teratomas and other neoplasms, present with psychiatric symptoms, seizures, memory deficits and decreased levels of consciousness. These symptoms often improve dramatically after immunotherapy or tumor resection. Here we review studies of the cellular and synaptic effects of these antibodies in hippocampal neurons in vitro and preliminary work in rodent models. Our work suggests that patient antibodies lead to rapid and reversible removal of neurotransmitter receptors from synaptic sites, leading to changes in synaptic and circuit function that in turn are likely to lead to behavioral deficits. We also discuss several of the many questions raised by these and related disorders. Determining the mechanisms underlying these novel anti-neurotransmitter receptor encephalopathies will provide insights into the cellular and synaptic bases of the memory and cognitive deficits that are hallmarks of these disorders, and potentially suggest avenues for therapeutic intervention.

[Lambert-Eaton myasthenic syndrome associated with pulmonary squamous cell carcinoma and circulating anti-P/Q-type voltage-gated calcium channel antibody]

We report a 64-year-old man diagnosed with Lambert-Eaton myasthenic syndrome (LEMS) associated with pulmonary squamous cell carcinoma. Circulating anti-P/Q-type voltage-gated calcium channel (VGCC) antibody was detected, and the patient was treated with 3,4-diaminopyridine. At age 61, chest radiograph revealed a tumor shadow in the right upper lung field. This was surgically removed, and a histological diagnosis of moderately differentiated pulmonary squamous cell carcinoma was obtained. After about 1 year, mediastinal metastasis was detected and 5-FU was administered. Eight months later, metastasis was noted in the left frontal hemisphere, and radiosurgical therapy was performed. The brain tumor gradually shrank but generalized fatigue, thirst, and gait disturbance developed after 4 months. A diagnosis of LEMS was made on the basis of neurological findings including proximal muscle weakness and absent tendon reflexes; autonomic symptoms (thirst, constipation, and impotence); characteristic electromyographic findings; and circulating anti-P/Q-type VGCC antibody. He has been treated with 3,4-diaminopyridine at a dose of 30 mg/day, resulting in marked improvement in symptoms but little change in electromyographic findings. The present case is very rare and suggests that anti-P/Q-type VGCC antibody may be involved in the mechanism of LEMS associated with pulmonary squamous cell carcinoma.

Calcium channels, neuromuscular synaptic transmission and neurological diseases

Voltage-dependent calcium channels are essential in neuronal signaling and synaptic transmission, and their functional alterations underlie numerous human disorders whether monogenic (e.g., ataxia, migraine, etc.) or autoimmune. We review recent work on Ca(V)2.1 or P/Q channelopathies, mostly using neuromuscular junction preparations, and focus specially on the functional hierarchy among the calcium channels recruited to mediate neurotransmitter release when Ca(V)2.1 channels are mutated or depleted. In either case, synaptic transmission is greatly compromised; evidently, none of the reported functional replacements with other calcium channels compensates fully.

Paraneoplastic neurological autoimmunity and survival in small-cell lung cancer

The autoimmune disorder of Lambert-Eaton myasthenic syndrome (LEMS) associates with small cell lung carcinoma (SCLC) in 50-60% of cases. It has been postulated that patients who harbour paraneoplastic neurological syndromes such as LEMS have an improved tumour prognosis compared to other patients with the tumour but without neurological deficit. In this intermediate report of an ongoing prospective study, 100 consecutive patients with biopsy-proven SCLC underwent full neurological examination and serum was taken for autoantibody analysis. Antibodies to voltage-gated calcium channels were detected in 10 patients, however only 4 had clinical and electrophysiological features of LEMS, 1 had limbic encephalitis, whilst the remaining 5 had no neurological signs. A further 6 patients had onconeural antibodies; only one had a paraneoplastic syndrome, sensory neuropathy. The median survival of the four antibody positive LEMS patients (19.6 months) was considerably greater than that for the antibody negative (8.9 months) or antibody positive patients as a whole (10.5 months). Although preliminary, these results suggest that functionally effective antibodies present in the sera of patients with LEMS may confer a survival advantage.

Lambert-Eaton myasthenic syndrome: search for alternative autoimmune targets and possible compensatory mechanisms based on presynaptic calcium homeostasis

The Lambert-Eaton myasthenic syndrome (LEMS) is a disease of neuromuscular transmission in which autoantibodies against the P/Q-type voltage-gated calcium channel (VGCC) at the presynaptic nerve terminal play a major role in decreasing quantal release of acetylcholine (ACh), resulting in skeletal muscle weakness and autonomic symptoms. It is associated with cancer, particularly small-cell lung carcinoma (SCLC), in 50-60% of LEMS patients; the nerve terminal and carcinoma cells apparently share a common antigen (VGCC), suggesting an immunological cross-reactivity that may lead to the neurological abnormality. Non-tumor LEMS has a strong association with HLA-DR3-B8. In approximately 15% of LEMS patients, no anti-P/Q-type VGCC antibodies are found, suggesting recognition of other targets(s). The VGCC-associated protein synaptotagmin could be one candidate, because it acts as an exocytotic calcium receptor, is implicated in fast ACh release; its N-terminus is exposed extracellularly during exocytosis and it is expressed in SCLC. Antibodies against synaptotagmin-1 were detected in both anti-VGCC-positive and -negative LEMS patients (20%), and it can be immunogenic, allowing induction of an animal model of LEMS. Another candidate target is the M1-type presynaptic muscarinic ACh receptor (M1 mAChR), also expressed extracellularly on motor nerve terminals; it modulates cholinergic transmission, linking to P/Q-type VGCC. In our series of 25 LEMS patients with and without SCLC, anti-M1 mAChR antibodies were prevalent in both anti-VGCC-positive and -negative LEMS patients. Autonomic symptoms seemed more frequent in the latter; serum from one of them passively transferred LEMS-type electrophysiological defects to mice. As a compensatory mechanism, researchers in Oxford suggested a shift in the dependence of ACh release from the P/Q-type to other types of VGCC. We have also focused on G protein-coupled mAChRs and neurotrophins, which may affect both P/Q-type VGCC and clathrin-independent "kiss-and-run" synaptic vesicle recycling (fast-mode of endocytosis) via protein kinase C activation. We hypothesize that these signaling cascades help to compensate for the immune-mediated defects in calcium entry in LEMS, compensation that may frequently be restricted by the coincident anti-M1 mAChR antibodies in this disease.

Calcium channelopathies: voltage-gated calcium channels

Since the initial identification of native calcium currents, significant progress has been made towards our understanding of the molecular and cellular contributions of voltage-gated calcium channels in multiple physiological processes. Moreover, we are beginning to comprehend their pathophysiological roles through both naturally occurring channelopathies in humans and mice and through targeted gene deletions. The data illustrate that small perturbations in voltage-gated calcium channel function induced by genetic alterations can affect a wide variety of mammalian developmental, physiological and behavioral functions. At least in those instances wherein the channelopathies can be attributed to gain-of-function mechanisms, the data point towards new therapeutic strategies for developing highly selective calcium channel antagonists.

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.

Syndrome de Lambert-Eaton et neuroblastome chez l'enfant : à propos de 2 observations

Lambert-Eaton myasthenic syndrome is a paraneoplasic syndrome which can reveal a primitive tumor. Frequently, the first diagnosis is myasthenia gravis. This disease is extremely rare in children. Only 10 cases have been reported in the last 35 years. We report 2 new observations occurring in very young patients, aged 2 and 3 years, with a ganglioneurobastoma as primitive tumor.

Phoneutria nigriventer ω-Phonetoxin IIA: A new tool for anti-calcium channel autoantibody assays in Lambert–Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is a neurological autoimmune disease in which downregulation of voltage-gated calcium channels (VGCCs) leads to reduced acetylcholine release from motoneuron terminals. 70% of cases are paraneoplastic and rapid diagnosis of LEMS can result in early detection of the underlying tumor. Serological assays based on the capacity of autoantibodies to precipitate VGCCs labeled with radioligands provide valuable data. We have established a novel assay using the spider venom peptide 125I-omega-Phonetoxin IIA (125I-omegaPtxIIA). 125I-omegaPtxIIA labeled recombinant Cav2.1 and Cav2.2 channels and endogenous VGCCs in rat brain membranes. Autoantibodies that immunoprecipitate a 125I-omegaPtxIIA/channel complex were detected in 26/31 (84%) LEMS patients. The patients that were seropositive in the 125I-omegaPtxIIA assay corresponded precisely to the population that was positive for Cav2.1 and/or Cav2.2 antibodies detected using two different omega-conotoxins. Thus, the 125I-omegaPtxIIA assay detects a broader spectrum of autoantibody specificities than current omega-conotoxin-based assays.

P/Q-type calcium channel antibodies, Lambert-Eaton myasthenic syndrome and survival in small cell lung cancer

To assess the survival impact of the presence of P/Q-type calcium channel antibodies in patients with small cell lung carcinoma (SCLC), we examined the frequency of the antibodies and Lambert-Eaton myasthenic syndrome (LEMS) in 148 consecutive patients with SCLC, and in 30 patients with paraneoplastic cerebellar degeneration and SCLC, and studied their relation with survival. In both series, only patients with LEMS had a remarkably long survival, whereas presence of the antibodies without LEMS did not result in a better prognosis.

Associated autoimmune diseases in patients with the Lambert-Eaton myasthenic syndrome and their families

In view of the clustering of autoimmune diseases (AIDs), we studied the frequency and nature of additional AIDs in patients with the Lambert-Eaton myasthenic syndrome (LEMS) and their family members, in both small cell lung carcinoma (SCLC) related and non-tumour (NT) related cases. Additional AIDs in patients with LEMS were assessed by interviewing the patient and studying the medical record. Family histories up to second-degree family members were established by interviewing patients, controls and family members. Forty-four patients with LEMS were assessed, of whom eighteen (41%) had SCLC. In the NT group seven patients (27%) had an additional AID, in the SCLC group two (11 %) (p=0.20). Thyroid disorder (five patients) and insulin dependent diabetes mellitus (two patients) were the most common AIDs. AIDs were significantly more frequent in families of patients with NT-LEMS (64%) than in control families (27%) (p=0.002), which was not found in SCLC-LEMS (36%, p=0.53). Affected family members were linked to the NT-LEMS patient through the maternal line in all cases. In conclusion, AIDs were more frequently found in LEMS patients without a tumour and their families, which could not be shown for SCLC-LEMS. This suggests that NT-LEMS shares immunogenetic factors with other AIDs. In families of NT-LEMS, a remarkable preponderance of maternal inheritance was seen, as has been reported previously in myasthenia gravis.

Dosage et spécificité d’autoanticorps anti-canaux calcium dans le syndrome myasthénique de Lambert-Eaton

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune channelopathy in which patients produce autoantibodies directed against voltage-gated calcium channels. Autoantibodies down-regulate calcium channels resulting in reduced transmitter release, which in turn leads to muscular weakness and autonomic dysfunction. LEMS is paraneoplastic in 60-70% of patients, most frequently associated with small cell lung carcinoma (SCLC). SCLC lines express many neuronal and neuroendocrine proteins including neuronal calcium channels of the Cav2 family (P/Q and N-type channels). It is thus likely that the paraneoplastic form of LEMS is the consequence of an anti-tumoral immune response and the production of antibodies that cross-react with identical or homologous antigens in nerve terminals. Neurological symptoms generally appear several Months before detection of the tumor. Consequently correct diagnosis of LEMS is crucial as it can allow early treatment of a particularly aggressive carcinoma. Based on published studies, our laboratory has set-up serological assays for LEMS autoantibodies as an aid to diagnosis. Calcium channels in detergent extracts of rat brain or cerebellum membranes were labeled with radioligands specific for N-type (125I-omega conotoxin GVIA) or P/Q-type (125I-omega conotoxin MVIIC) calcium channels. Autoantibodies that immunoprecipitate the ligand/channel complex can thus be titrated. Analysis of 31 LEMS sera revealed the presence of anti-N type channel antibodies in 58% and anti-P/Q type channel antibodies in 74% of patients with titres ranging from 90 to 2950 pM. Only 5 patients were seronegative in both tests, thus a combination of the two assays reliably detected autoantibodies in 26/31 (84%) patients.

Pathogenic Autoantibodies in the Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder of neuromuscular transmission in which antibodies are directed against voltage-gated calcium channels (VGCCs). We studied the action of LEMS immunoglobulin G (IgG) on cloned human VGCCs stably transfected into human embryonic kidney cells (HEK293). All LEMS IgGs tested bound to the surface of the P/Q-type VGCC cell line and caused a significant reduction in whole-cell calcium currents in these cells. By contrast, only 2 out of 6 IgGs bound extracellularly to the N-type VGCC cell line, and none of the LEMS IgGs tested was able to reduce whole-cell calcium currents in these cells. We used this apparent specificity of LEMS IgG for the P/Q-type VGCC to investigate the action of these IgGs on model systems where a number of different VGCC populations exist in equilibrium. LEMS IgG caused a significant downregulation in the omega-agatoxin IVA-sensitive P/Q-type VGCCs of cultured rat cerebellar neurons, but this was accompanied by a concomitant rise in the "resistant" R-type VGCCs. By using the passive transfer model of LEMS, similar results were observed at the mouse neuromuscular junction, where a significant reduction in P/Q-type VGCCs was paralleled by an increase in L- and R-type VGCCs. These results demonstrate an unexpected plasticity in the expression of VGCCs in mammalian neurons and may represent a mechanism by which the pathogenic effects of LEMS IgG are reduced.