The action of amyotrophic lateral sclerosis immunoglobulins on mammalian single skeletal muscle Ca2+ channels

Passive Transfer of Blood Sera from ALS Patients with Identified Mutations Results in Elevated Motoneuronal Calcium Level and Loss of Motor Neurons in the Spinal Cord of Mice

Introduction: Previously, we demonstrated the degeneration of axon terminals in mice after repeated injections of blood sera from amyotrophic lateral sclerosis (ALS) patients with identified mutations. However, whether a similar treatment affects the cell body of motor neurons (MNs) remained unresolved. Methods: Sera from healthy individuals or ALS patients with a mutation in different ALS-related genes were intraperitoneally injected into ten-week-old male Balb/c mice (n = 3/serum) for two days. Afterward, the perikaryal calcium level was measured using electron microscopy. Furthermore, the optical disector method was used to evaluate the number of lumbar MNs. Results: The cytoplasmic calcium level of the lumbar MNs of the ALS-serum-treated mice, compared to untreated and healthy-serum-treated controls, was significantly elevated. While injections of the healthy serum did not reduce the number of MNs compared to the untreated control group, ALS sera induced a remarkable loss of MNs. Discussion: Similarly to the distant motor axon terminals, the injection of blood sera of ALS patients has a rapid degenerative effect on MNs. Analogously, the magnitude of the evoked changes was specific to the type of mutation; furthermore, the degeneration was most pronounced in the group treated with sera from ALS patients with a mutation in the chromosome 9 open reading frame 72 gene.

Passive Transfer of Sera from ALS Patients with Identified Mutations Evokes an Increased Synaptic Vesicle Number and Elevation of Calcium Levels in Motor Axon Terminals, Similar to Sera from Sporadic Patients

Previously, we demonstrated increased calcium levels and synaptic vesicle densities in the motor axon terminals (MATs) of sporadic amyotrophic lateral sclerosis (ALS) patients. Such alterations could be conferred to mice with an intraperitoneal injection of sera from these patients or with purified immunoglobulin G. Later, we confirmed the presence of similar alterations in the superoxide dismutase 1 G93A transgenic mouse strain model of familial ALS. These consistent observations suggested that calcium plays a central role in the pathomechanism of ALS. This may be further reinforced by completing a similar analytical study of the MATs of ALS patients with identified mutations. However, due to the low yield of muscle biopsy samples containing MATs, and the low incidence of ALS patients with the identified mutations, these examinations are not technically feasible. Alternatively, a passive transfer of sera from ALS patients with known mutations was used, and the MATs of the inoculated mice were tested for alterations in their calcium homeostasis and synaptic activity. Patients with 11 different ALS-related mutations participated in the study. Intraperitoneal injection of sera from these patients on two consecutive days resulted in elevated intracellular calcium levels and increased vesicle densities in the MATs of mice, which is comparable to the effect of the passive transfer from sporadic patients. Our results support the idea that the pathomechanism underlying the identical manifestation of the disease with or without identified mutations is based on a common final pathway, in which increasing calcium levels play a central role.

Calcium in the pathomechanism of amyotrophic lateral sclerosis - Taking center stage?

Amyotrophic lateral sclerosis is an incurable, relentlessly progressive disease primarily affecting motor neurons. The cause of the disease, except for the mutations identified in a small fraction of patients, is unknown. The major mechanisms contributing to the degeneration of motor neurons have already been disclosed and characterized, including excitotoxicity, oxidative stress, mitochondrial dysfunction, and immune/inflammatory processes. During the progression of the disease these toxic processes are not discrete, but each facilitates the deleterious effect of the other. However, due to their common reciprocal calcium dependence, calcium ions may act as a common denominator and through a positive feedback loop may combine the individual pathological processes into a unified escalating mechanism of neuronal destruction. This mini-review provides an overview of the mutual calcium dependence of the major toxic mechanisms associated with amyotrophic lateral sclerosis.

Progressive impairment of CaV1.1 function in the skeletal muscle of mice expressing a mutant type 1 Cu/Zn superoxide dismutase (G93A) linked to amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder that is typically fatal within 3–5 years of diagnosis. While motoneuron death is the defining characteristic of ALS, the events that underlie its pathology are not restricted to the nervous system. In this regard, ALS muscle atrophies and weakens significantly before presentation of neurological symptoms. Since the skeletal muscle L-type Ca²⁺ channel (Ca_V1.1) is a key regulator of both mass and force, we investigated whether Ca_V1.1 function is impaired in the muscle of two distinct mouse models carrying an ALS-linked mutation.

Methods

We recorded L-type currents, charge movements, and myoplasmic Ca²⁺ transients from dissociated flexor digitorum brevis (FDB) fibers to assess Ca_V1.1 function in two mouse models expressing a type 1 Cu/Zn superoxide dismutase mutant (SOD1^G93A).

Results

In FDB fibers obtained from “symptomatic” global SOD1^G93A mice, we observed a substantial reduction of SR Ca²⁺ release in response to depolarization relative to fibers harvested from age-matched control mice. L-type current and charge movement were both reduced by ~40 % in symptomatic SOD1^G93A fibers when compared to control fibers. Ca²⁺ transients were not significantly reduced in similar experiments performed with FDB fibers obtained from “early-symptomatic” SOD1^G93A mice, but L-type current and charge movement were decreased (~30 and ~20 %, respectively). Reductions in SR Ca²⁺ release (~35 %), L-type current (~20 %), and charge movement (~15 %) were also observed in fibers obtained from another model where SOD1^G93A expression was restricted to skeletal muscle.

Conclusions

We report reductions in EC coupling, L-type current density, and charge movement in FDB fibers obtained from symptomatic global SOD1^G93A mice. Experiments performed with FDB fibers obtained from early-symptomatic SOD1^G93A and skeletal muscle autonomous MLC/SOD1^G93A mice support the idea that events occurring locally in the skeletal muscle contribute to the impairment of Ca_V1.1 function in ALS muscle independently of innervation status.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-016-0094-6) contains supplementary material, which is available to authorized users.

Serine proteases purified from sera of patients with amyotrophic lateral sclerosis (ALS) induce contrasting cytopathology in murine motoneurones to IgG

Affinity purified IgG from sera of patients with amyotrophic lateral sclerosis (ALS) is claimed to enhance transmitter release, induce apoptotic death of cultured motoneurones, and elicit a distinctive cytopathology with raised Ca(2+) in mouse motoneurones. An alternative hypothesis attributes these events to serine proteases in ALS sera. To test this, motoneurones in BALB/c mice injected intraperitoneally with plasminogen affinity purified from sera of ALS patients and healthy controls were analysed using immunochemical and ultrastructural morphometric methods. The responses were validated in motoneurones of mice injected with commercially purified plasminogen, tissue plasminogen activator (tPA), or plasmin. Motoneurones in non-injected mice had normal morphology and ultrastructure without evidence of electron-dense degeneration. Purified plasminogen from both ALS patients and healthy controls, evoked electron-dense motoneurone degeneration, as did commercially purified plasminogen and tPA. The common cytopathology comprised disruption and distension of Nissl body rough endoplasmic reticulum, cytoplasmic polyribosomal proliferation, and significant Ca(2+) enhancement in mitochondria. By contrast, using affinity purified serum immunoglobulins, ALS-IgG but not IgG from healthy or disease controls, elicited necrosis, with 30% of ALS-IgGs tested evoking electron-dense degeneration in 40% of motoneurones. The primary cytopathology was extensive swelling of Golgi endoplasmic reticulum and mitochondria, with enhancement of Ca(2+) in Golgi endoplasmic reticulum and presynaptic boutons. We conclude that serine proteases purified from sera of ALS patients elicits a distinctive cytopathology and pattern of Ca(2+) enhancement in motoneurones different from that found on passive transfer of affinity purified ALS-IgG.

Amyotrophic lateral sclerosis patient IgG alters voltage dependence of Ca2+ channels in dissociated rat motoneurons

Previous studies on sporadic amyotrophic lateral sclerosis (SALS) have detected IgG within motoneurons of patients and these IgGs have been shown to alter voltage dependent calcium channel activity in various cell types. The current study investigates whether IgG from categorized SALS patients alter voltage dependent calcium currents in rat motoneurons in culture. Patients were categorized based on onset and progression pattern. IgG yields were 38% higher in SALS patients compared to control subjects. Incubation with 1 mg/ml IgG from SALS patients did not cause visible toxicity, alter input resistance, capacitance or the maximal calcium conductance in rat motoneurons when compared to motoneurons incubated with control IgG. However, the activation curve of calcium current was shifted to the left in motoneurons treated with SALS IgG compared to control IgG.

Ultrastructural analysis of spinal motoneurones from mice treated with IgG from ALS patients, healthy individuals, or disease controls

Reports that ALS-IgG injected into mice results in ultrastructural abnormalities and enhanced deposition of Ca(2+) in their spinal motoneurones are unverified. To obtain verification, affinity purified IgG's from ten healthy subjects, seventeen ALS patients and eight disease controls (e.g. cases of LEMS, MS,) were injected into groups of mice in 4 daily doses by either i/m injection, or i/p (Total doses, 2-4 mg i/p, 1 mg i/m). Immunocytochemistry identified human IgG in lumbar motoneurones 48 h after the final dose. Their morphology was examined by EM and intraneuronal Ca2+ was revealed by oxylate-pyroantimonate histochemistry and its identity verified by 2 degrees emission spectroscopy. In the EM, motoneurones of non-injected mice, and mice receiving healthy IgGs had a lucent cytoplasm, intact mitochondria, and Golgi complexes comprising stacks of narrow ER. About 40% of Nissl bodies comprised alternate rER lamellae and polyribosome arrays (Type 1 structure): 10% formed polyribosome clusters (Type 3). Mitochondria, Golgi ER and presynaptic terminals contained Ca(2+) associated pyroantimonate. I/m and i/p ALS-IgG produced similar results. Some ALS IgGs (i.e. patients) produced electron dense degenerative cytology: all promoted fragmented and distended Golgi ER, polyribosmal hyperplasia, reduced numbers of Type I but raised numbers of Types 2 and 3 Nissl bodies, and a greater proportion of Golgi ER and presynaptic terminals containing Ca(2+)-antimonate. With 4/8 disease control IgGs motoneurones had normal Golgi and Nissl body organisation but dilated rER. Ca2+ content was normal. Remaining IgGs produced normal ultrastructure. Results support claims that ALS-IgG may be cytotoxic, and that it enhances the Ca(2+) content of motoneurones and synaptic terminals.

Amyotrophic lateral sclerosis and occupational exposure to electromagnetic fields

In an hypothesis-generating case-control study of amyotrophic lateral sclerosis, lifetime occupational histories were obtained. The patients (n = 28) were clinic based. The occupational exposure of interest in this report is electromagnetic fields (EMFs). This is the first and so far the only exposure analyzed in this study. Occupational exposure up to 2 years prior to estimated disease symptom onset was used for construction of exposure indices for cases. Controls (n = 32) were blood and nonblood relatives of cases. Occupational exposure for controls was through the same age as exposure for the corresponding cases. Twenty (71%) cases and 28 (88%) controls had at least 20 years of work experience covering the exposure period. The occupational history and task data were used to classify blindly each occupation for each subject as having high, medium/high, medium, medium/low, or low EMF exposure, based primarily on data from an earlier and unrelated study designed to obtain occupational EMF exposure information on workers in "electrical" and "nonelectrical" jobs. By using the length of time each subject spent in each occupation through the exposure period, two indices of exposure were constructed: total occupational exposure (E1) and average occupational exposure (E2). For cases and controls with at least 20 years of work experience, the odds ratio (OR) for exposure at the 75th percentile of the E1 case exposure data relative to minimum exposure was 7.5 (P < 0.02; 95% CI, 1.4-38.1) and the corresponding OR for E2 was 5.5 (P < 0.02; 95% CI, 1.3-22.5). For all cases and controls, the ORs were 2.5 (P < 0.1; 95% CI, 0.9-8.1) for E1 and 2.3 (P = 0.12; 95% CI, 0.8-6.6) for E2. This study should be considered an hypothesis-generating study. Larger studies, using incident cases and improved exposure assessment, should be undertaken.

Characterization of Ca(2+)-channels responsible for K(+)-evoked [(3)H]noradrenaline release from rat brain cortex synaptosomes and their response to amyotrophic lateral sclerosis IgGs

The contribution of the different Ca(2+)-channel subtypes to the K(+)-evoked [(3)H]noradrenaline release from rat cerebral cortex synaptosomes has been investigated. In the same experimental model, it was also verified whether the calcium-mediated neurotransmitter release is influenced by IgGs purified from sera of seven patients affected by sporadic amyotrophic lateral sclerosis. Synaptosome treatment with 3.0 microM nifedipine or 2.0 microM calciseptine, which block L-type channels, slightly decreased [(3)H]noradrenaline release, the reduction being 7 and 13% of the control values, respectively. The blockade of N-type Ca(2+)-channels with omega-conotoxin-GVIA (0.001-1.0 microM) induced a concentration-dependent reduction of the neurotransmitter release, with maximum effect of 34%. omega-Agatoxin-IVA failed to significantly affect the studied release, which was instead markedly reduced by omega-conotoxin-MVIIC. After the blockade of N-type channels with maximal concentrations of omega-conotoxin-GVIA, 3.0 microM omega-conotoxin-MVIIC reduced the release by 58%. Synaptosome treatment with amyotrophic lateral sclerosis IgGs enhanced the K(+)-evoked [(3)H]noradrenaline release, which was mostly mediated by P/Q- and N-type Ca(2+)-channels. The increase induced by pathologic IgGs (0.2 mg/ml) ranged from 11 to 62% for the different patients, and it was concentration-dependent. The basal release was instead unaffected by IgG treatment. The results of the present study suggest that the K(+)-evoked [(3)H]noradrenaline release from brain cortex synaptosomes is mainly mediated by activation of P/Q- and N-type Ca(2+)-channels. Autoantibodies present in the sera of patients affected by sporadic amyotrophic lateral sclerosis may interact with these channels by producing an increased calcium influx, with consequent enhancement of the neurotransmitter release. Preliminary results of the present study have been published in abstract form (Martire et al., 1997, Pharmacol. Res. 35:9).

Electromechanical coupling and synchronous firing of single wrist extensor motor units in sporadic amyotrophic lateral sclerosis

Electrical and contractile properties of motor units (MU) were studied in the extensor carpi radialis muscles during voluntary contraction. The discharge of 234 single MUs was recorded in 11 patients with sporadic amyotrophic lateral sclerosis (ALS) and compared with that of the 260 MUs recorded in 12 healthy control subjects. Characteristics of the MU twitches and of the macro-potentials, the electromechanical coupling and the synchronization of the motor neurone discharges, were compared. In 5 patients (population ALS1), the twitch contraction force and macro-MUP area values were much larger than those of the controls. In the 6 other patients (population ALS2), the twitch force was considerably depressed, whereas the macro-MUP area was slightly, but significantly, increased. In ALS1, as well as in ALS2, the electromechanical coupling was much weaker than in the controls, and the fast-contracting MUs were more severely affected than the slowly contracting MUs. The motoneuronal synchronization was assessed by performing cross-correlation analysis on MUs discharges, and was used as an index to the strength of the common motoneuronal inputs. The rate of occurrence of synchronous firing was conspicuously lower in both populations of patients than in the control group. This might reflect the loss of corticospinal projections that occurs in ALS. The data are discussed in terms of the time course of motor neurone axonal sprouting, and in terms of the neuronal and muscular dysfunction possibly involved in ALS disease.

Sera from amyotrophic lateral sclerosis patients reduce high-voltage activated Ca2+ currents in mice dorsal root ganglion neurons

This study investigated the effects of sera from amyotrophic lateral sclerosis (ALS) patients on high voltage activated (HVA) Ca2+ current in mice dorsal root ganglion (DRG) cells using whole-cell voltage-clamp method. Mice were injected with sera from healthy adults, from patients with other neurological diseases, and from patients with the sporadic form of ALS, for a period of 3 days. Sera from five of six ALS patients reduced HVA Ca2+ current amplitude. The peak Ca2+ current was significantly reduced by ALS sera while the sera from healthy adults and patients with other diseases did not alter Ca2+ current. The inactivation kinetics was altered by ALS sera, and the half-inactivation voltage shifted to more negative potential in ALS group. These results suggest that sporadic ALS serum factors may exert interactions with the HVA Ca2+ channel in DRG cells to reduce the Ca2+ current.

Ultrastructural evidence for altered calcium in motor nerve terminals in amyotropic lateral sclerosis

Numerous studies of amyotrophic lateral sclerosis have suggested that increased intracellular calcium is a common denominator in motoneuron injury. In experimental models, IgG from patients with amyotrophic lateral sclerosis enhanced calcium entry and induced apoptotic cell death in vitro as well as increased intracellular calcium and induced ultrastructural alterations of the motor nerve terminals in mice in vivo. To determine whether similar increases in intracellular calcium and altered morphology are present in motor nerve terminals of amyotrophic lateral sclerosis patients in vivo, muscle biopsy specimens from 7 patients with amyotrophic lateral sclerosis, 10 nondenervating disease control subjects, and 5 patients with denervating neuropathies were analyzed with ultrastructural techniques, employing oxalate-pyroantimonate fixation to preserve in situ calcium distribution. Motor nerve terminals from amyotrophic lateral sclerosis specimens contained significantly increased calcium, increased mitochondrial volume, and increased numbers of synaptic vesicles compared to any of the disease control groups, without exhibiting excess Schwann envelopment specific to denervating terminals. These results parallel the effect of amyotrophic lateral sclerosis IgG passively transferred to mice, and provide the first demonstration that neuronal calcium is, in fact, increased in amyotrophic lateral sclerosis in vivo.

Altered muscle calcium channel binding kinetics in autoimmune motoneuron disease

While skeletal muscle is not apparently affected directly in amyotrophic lateral sclerosis (ALS), immunoglobulin G fractions purified from patients with ALS (ALS IgG) bind dihydropyridine (DHP)-sensitive L-type voltage-gated calcium channel (VGCC) antigen isolated from skeletal muscle in ELISA and Western immunoblot, and alter VGCC function in vitro. To determine whether muscle VGCC properties are altered in ALS, VGCC-enriched subsarcolemmal membrane fractions were prepared from biopsied quadriceps muscle of patients with ALS, with other neurologic diseases, or without apparent muscle disease, and tested for DHP binding with [3H]PN200-110. ALS muscle VGCCs possessed eightfold higher binding affinities for [3H]PN200-110 than did VGCCs from muscle fractions of most other patients, independent of denervation-induced increases in DHP binding site number. Similarly elevated DHP binding affinities were observed in specimens from patients with autoimmune motor neuropathies, suggesting that ALS and immune mediated motoneuron disease share skeletal muscle L-type VGCC alterations.

Molecular approaches to amyotrophic lateral sclerosis

New discoveries are expanding our knowledge of mechanisms involved in amyotrophic lateral sclerosis (ALS) pathogenesis. Some recent advances in our understanding of motoneuron death in familial ALS (fALS) and sporadic ALS (sALS) are reviewed, with emphasis on molecular similarities that may further unite these phenotypically linked diseases.

The role of calcium-binding proteins in selective motoneuron vulnerability in amyotrophic lateral sclerosis

The factors contributing to selective motoneuron loss in amyotrophic lateral sclerosis (ALS) remain undefined. To investigate whether calcium-binding proteins contribute to selective motoneuron vulnerability in ALS, we compared calbindin-D28K and parvalbumin immunoreactivity in motoneuron populations in human ALS, and in a ventral spinal cord hybrid cell line selectively vulnerable to the cytotoxic effects of ALS IgG. In human autopsy specimens, immunoreactive calbindin-D28k and parvalbumin were absent in motoneuron populations lost early in ALS (i.e., cortical and spinal motoneurons, lower cranial nerve motoneurons), while motoneurons damaged late or infrequently in the disease (i.e., Onuf's nucleus motoneurons, oculomotor, trochlear, and abducens nerve neurons) expressed markedly higher levels of immunoreactive calbindin-D28K and/or parvalbumin. Motoneuron-neuroblastoma VSC 4.1 hybrid cells lost immunoreactive calbindin-D28k and parvalbumin following dibutyryl-cyclic AMP-induced differentiation and were killed by IgG from ALS patients. Undifferentiated calbindin/parvalbumin-reactive VSC 4.1 cells were not killed, nor were other cell lines expressing high levels of calbindin-D28K and parvalbumin immunoreactivity (substantia nigra-neuroblastoma hybrid cells and N18TG2 neuroblastoma parent cells). These studies suggest that decreased calbindin-D28K and parvalbumin immunoreactivity may help explain the selective vulnerability of motoneurons in ALS.

Evidence for autoimmunity in amyotrophic lateral sclerosis

Although the etiology and pathogenesis of ALS is unknown, increasing evidence supports a role for autoimmune mechanisms in motoneuron degeneration and death. An animal model, experimental autoimmune gray matter disease, can be induced by the inoculation of spinal cord gray matter. The experimental disease is characterized by weakness secondary to the loss of upper and lower motoneurons, accompanied by inflammatory foci within the spinal cord, and IgG at the neuromuscular junction and within UMN and LMN. In human ALS, IgG is present within the UMN and LMN, and T-lymphocytes and activated microglia have been identified within spinal cord gray matter and motor cortex. ALS IgG can passively transfer physiological changes of the neuromuscular junction to mice resulting in enhanced release of acetylcholine. The ALS IgG selectively interact with calcium channels and alter channel function. These data suggest a potential role for autoimmune mechanisms in the destruction and loss of motoneurons in ALS.

Cytotoxicity of immunoglobulins from amyotrophic lateral sclerosis patients on a hybrid motoneuron cell line

Patients with amyotrophic lateral sclerosis possess antibodies (ALS IgGs) that bind to L-type skeletal muscle voltage-gated calcium channels (VGCCs) and inhibit L-type calcium current. To determine whether interaction of ALS IgGs with neuronal VGCCs might influence motoneuron survival, we used a motoneuron-neuroblastoma hybrid (VSC 4.1) cell line expressing binding sites for inhibitors of L-, N-, and P-type VGCCs. Using direct viable cell counts, quantitation of propidium iodide- and fluorescein diacetate-labeled cells, and lactate dehydrogenase release to assess cell survival, we document that ALS IgG kills 40-70% of cAMP-differentiated VSC 4.1 cells within 2 days. ALS IgG-mediated cytotoxicity is dependent on extracellular calcium and is prevented by peptide antagonists of N- or P-type VGCCs but not by dihydropyridine modulators of L-type VGCCs. Preincubating IgG with purified intact L-type VGCC or with isolated VGCC alpha 1 subunit also blocks ALS IgG-mediated cytotoxicity. These results suggest that ALS IgG may directly lead to motoneuron cell death by a mechanism requiring extracellular calcium and mediated by neuronal-type calcium channels.

Amyotrophic lateral sclerosis patient antibodies label Ca2+ channel alpha 1 subunit

Sporadic amyotrophic lateral sclerosis is an idiopathic human degenerative disease of spinal cord and brain motor neurons. Prior studies demonstrated that most patients with amyotrophic lateral sclerosis possess immunoglobulins that bind to purified L-type voltage-gated calcium channels, that titers of anti-voltage-gated calcium channel antibodies correlate with disease progression rates, and that amyotrophic lateral sclerosis patient-derived antibodies (ALS IgG) produce electrophysiological changes in the function of voltage-gated calcium channels. Using Western transfer immunoblots and enzyme-linked immunosorbent assays, the calcium ionophore-forming alpha 1 subunit of the voltage-gated calcium channel is now identified as the major voltage-gated calcium channel antigen to which ALS IgG binds. Additionally, the binding of an L-type voltage-gated calcium channel alpha 1 subunit-directed monoclonal antibody, which itself mimics the effects of ALS IgG on skeletal muscle voltage-gated calcium channel currents, is selectively prevented by preaddition of ALS IgG. Voltage-gated calcium channel-binding IgG from patients with Lambert-Eaton myasthenic syndrome appears to be differentiated from ALS IgG by the reactivity of the former to both alpha 1 and beta subunits of the calcium channel. These assays provide further evidence linking amyotrophic lateral sclerosis to an autoimmune process, and suggest one means to differentiate immunoglobulins from patients with amyotrophic lateral sclerosis from those of patients with another autoimmune disease expressing calcium channel antibodies.

Effects of diltiazem upon a rapidly exchanging calcium compartment related to repriming in frog skeletal muscle

Following spontaneous relaxation, fast skeletal muscle must first repolarize and then undergo a first-order repriming reaction before depolarization will result in maximal tension production. 45Ca exposure during repriming defined two Ca compartments during subsequent efflux, named Ca(fast) and Ca(fast). Ca(slow) had an average time constant of 112 +/- 17 min. On the basis of slow turnover and content determined by a variety of methods, I suggest Ca(slow) represents Ca within the sarcoplasmic reticulum. Ca(fast) contained 12 pmol Ca per fibre and resting exchange had a time constant of 5.1 +/- 0.4 min. A total of 12 pmol 45Ca within Ca(fast) was released during a maximal contracture. Most of the Ca released from Ca(fast) rapidly entered the extracellular space; however, 0.39 +/- 0.15 pmol Ca per fibre transferred from Ca(fast) into Ca(slow) when the muscle bundle contracted. When 1-10 microM diltiazem reduced contracture time-tension, release of Ca(fast) was reduced proportionally. When 10 microM diltiazem paralyzed excitation-contraction coupling, Ca(fast) was not released. Refilling of Ca(fast) was proportional to the extent of repriming during 45Ca exposure. Although release and refilling of Ca(fast) is related to contraction, its role in excitation-contraction coupling remains to be elucidated.

IgG from amyotrophic lateral sclerosis patients increases current through P-type calcium channels in mammalian cerebellar Purkinje cells and in isolated channel protein in lipid bilayer

The effect of the IgG from amyotrophic lateral sclerosis (ALS) patients was tested on the voltage-dependent barium currents (IBa) in mammalian dissociated Purkinje cells and in isolated P-type calcium channels in lipid bilayers. Whole cell clamp of Purkinje cells demonstrates that ALS IgG increases the amplitude of IBa without modifying their voltage kinetics. This increased IBa could be blocked by a purified nonpeptide toxin from Agelenopsis aperta venom (purified funnel-web spider toxin) or by a synthetic polyamine analog (synthetic funnel-web spider toxin) and by a peptide toxin from the same spider venom, omega-Aga-IVA. Similar results were obtained on single-channel recordings from purified P channel protein. The addition of ALS IgG increased single-channel IBa open time without affecting slope conductance. The results described above were not seen with normal human IgG nor with boiled ALS IgG. It is concluded that ALS IgG enhances inward current through P-type calcium channels. Since P-type Ca2+ channels are present in motoneuron axon terminals, we propose that the enhanced calcium current triggered by ALS IgG may contribute to neuronal damage in ALS.

Evidence for autoimmunity in amyotrophic lateral sclerosis

Although the etiology and pathogenesis of ALS is unknown, increasing evidence supports a role for autoimmune mechanisms in motoneuron degeneration and death. An animal model, experimental autoimmune gray matter disease, can be induced by the inoculation of spinal cord gray matter. The experimental disease is characterized by weakness secondary to the loss of upper and lower motoneurons, accompanied by inflammatory foci within the spinal cord, and IgG at the neuromuscular junction and within UMN and LMN. In human ALS, IgG is present within the UMN and LMN, and T-lymphocytes and activated microglia have been identified within spinal cord gray matter and motor cortex. ALS IgG can passively transfer physiological changes of the neuromuscular junction to mice resulting in enhanced release of acetylcholine. The ALS IgG selectively interact with calcium channels and alter channel function. These data suggest a potential role for autoimmune mechanisms in the destruction and loss of motoneurons in ALS.