The chemotherapeutic oxaliplatin alters voltage-gated Na(+) channel kinetics on rat sensory neurons

The chemotherapeutic oxaliplatin causes a sensory-motor neuropathy with predominantly hyperpathic symptoms. The mechanism underlying this hyperexcitability was investigated using rat sensory nerve preparations, dorsal root ganglia and hippocampal neurons. Oxaliplatin resulted in an increase of the amplitude and duration of compound action potentials. It lengthened the refractory period of peripheral nerves suggesting an interaction with voltage-gated Na(+) channels. Application of oxaliplatin to dorsal root ganglion neurons resulted in an increase of the Na(+) current, a block of the maximal amplitude and a shift of the voltage-response relationship towards more negative membrane potentials. The effect was detectable on 13 of 18 tested cells. This observation, together with the absence of any effect on Na(+) currents of hippocampal neurons, suggests that the interaction of oxaliplatin is restricted to one or more channel subtypes. The effect of oxaliplatin could be antagonised by the Na(+) channel blocker carbamazepine which could be used to reduce side effects of oxaliplatin therapy in patients.

Calcium potentials and tetrodotoxin-resistant sodium potentials in unmyelinated C fibres of biopsied human sural nerve

Compound action potentials and electrotonic responses to 150 ms current pulses were recorded from isolated nerve fascicles of human sural nerve biopsies. Compound action potentials in normal bathing solution were characterized by previously described A beta, A delta and C fibre components. In addition, tetrodotoxin-resistant sodium- or calcium-dependent potential components were found when a mixture of tetrodotoxin and the potassium channel blockers 4-aminopyridine and tetraethylammonium was added to the bathing solution. In contrast to tetrodotoxin-sensitive action potentials, tetrodotoxin-resistant sodium- or calcium-dependent potentials could be recorded in the presence of high extracellular potassium concentrations (10-20 mM). Calcium action potentials were found to be sensitive to specific pharmacological antagonists or agonists of L-, N- and P-type calcium channels. Lidocaine, cadmium, verapamil and capsaicin showed unspecific blocking effects on calcium and tetrodotoxin-resistant potentials. Tetrodotoxin-resistant action potentials seem to originate from unmyelinated C fibres since a clear correlation was found between the number of C fibres and the amplitude of tetrodotoxin-resistant calcium and sodium spikes in preparations with different axon type composition. The evidence for tetrodotoxin-resistant Na+ and Ca2+ spikes in peripheral human axons offers new possibilities for a better understanding and/or treatment of abnormalities in the excitability of damaged or diseased peripheral nerves.

Abnormal axonal inward rectification in diabetic neuropathy

An abnormal axonal membrane conductance might contribute to human diabetic neuropathy. To test this idea, we have compared the threshold changes produced by long-lasting (100-200 ms) de- and hyperpolarizing currents applied to median motor and sensory axons at the wrist in 63 diabetic patients with those from 50 normal controls and 27 amyotrophic lateral sclerosis (ALS) patients. Averages of the threshold electrotonus plots for motor and sensory axons of diabetic patients showed more subexcitability during, and slower recovery following, the application of hyperpolarizing currents. Such alterations have been previously found in isolated rat nerves after inhibition of axonal inward rectification by means of cesium ions. The abnormalities in diabetics were positively correlated with the age of patients and the presence of neuropathy. Threshold electrotonus seen in diabetes differed strongly from the effects of acute ischemia and were unlike changes recorded in ALS. The data indicate that an abnormal inward rectification of peripheral axons is associated with diabetic neuropathy. A better understanding of the neurobiology of this conductance might provide information about the pathophysiology of this disease.

Function of the hyperpolarization-activated inward rectification in nonmyelinated peripheral rat and human axons

The function of time-dependent, hyperpolarization-activated inward rectification was analyzed on compound potentials of nonmyelinated axons in the mammalian peripheral nervous system. Isolated rat vagus nerves and fascicles of biopsied human sural nerve were tested in a three-chambered, Vaseline-gap organ bath at 37 degrees C. Inward rectification was assessed by recording the effects of long-lasting hyperpolarizing currents on electrical excitability with the use of the method of threshold electrotonus (program QTRAC, copyright Institute of Neurology, London, UK) and by measuring activity-dependent changes in conduction velocity and membrane potential. Prominent time-dependent, cesium-sensitive inward rectification was revealed in rat vagus and human sural nerve by recording threshold electrotonus to 200-ms hyperpolarizing current pulses. A slowing of compound action potential conduction was observed during a gradual increase in the stimulation frequency from 0.1 to 3 Hz. Above a stimulation frequency of 0.3 Hz, this slowing of conduction was enhanced during bath application of 1 mM cesium. Cesium did not alter action potential waveforms during stimulation at frequencies < 1 Hz. Cesium-induced slowing in action potential conduction was correlated with membrane hyperpolarization. The hyperpolarization by cesium was stronger during higher stimulation frequencies and small in unstimulated nerves. These data show that a cesium-sensitive, time-dependent inward rectification in peripheral rat and human nonmyelinated nerve fibers limits the slowing in conduction seen in such axons at action potential frequencies higher than approximately 0.3 Hz.

Consequences of mutations within the C terminus of the FHL1 gene

BACKGROUND

Mutations in the four-and-a-half LIM domain 1 gene (FHL1) cause X-linked late-onset scapuloaxioperoneal myopathy characterized by postural muscle atrophy with rigid spine syndrome with pseudoathleticism/hypertrophy (XMPMA), reducing body myopathy (RBM), and scapuloperoneal myopathy. Divergences in these diseases are hitherto unclear; therefore, we searched for additional families to elucidate differences and similarities of these allelic FHL1opathies.

METHODS

Using genotyping and phenotyping (mutational analysis, muscle histopathology, and Western blotting) we characterized 10 affected men and 8 women from 7 families.

RESULTS

All patients displayed the XMPMA phenotype. In 1 family with a novel missense mutation, 2 affected men had an aneurysm of the sinus of Valsalva in addition. In 5 affected men and 2 affected women from 4 families, the C224W missense mutation in FHL1 was detected, which putatively disrupts the fourth LIM domain. In 3 other families with 5 affected men and 1 female, 2 novel missense variants and a novel splice-site mutation in the C terminus of FHL1 were found. Muscle morphology revealed mild to moderate degenerative myopathy with myofiber hypertrophy of both fiber types at younger age and cytoplasmic bodies in the majority of the samples. Reducing bodies, pathognomonic for RBM, were not found. Western blotting revealed no detectable FHL1A protein in our patients.

CONCLUSIONS

As a consequence of C terminal FHL1 gene mutations, the X-linked myopathy characterized by postural muscle atrophy (XMPMA) phenotype and morphotype with cytoplasmic bodies are found. In the spectrum of FHL1opathies, the preserved FHL1C protein is likely responsible for the moderate XMPMA phenotype compared with the more severe reducing body myopathy/scapuloperoneal myopathy phenotype.

X-linked dominant Charcot-Marie-Tooth neuropathy: clinical, electrophysiological, and morphological phenotype in four families with different connexin32 mutations(1)

The sensorimotor neuropathy of the Charcot-Marie-Tooth type (CMT) is the most common hereditary disorder of the peripheral nervous system. The X-linked dominant form of CMT (CMTX) is associated with mutations in the gene for the gap junction protein connexin32. We examined four CMTX pedigrees two of which had potentially novel mutations in the only coding exon of connexin32. One previously unreported missense mutation, Ala39Val, was found in a family displaying a CMT phenotype with additional upper limb postural tremor reminiscent of a Roussy-Lévy syndrome. A novel single base insertion, 679insT, is among the first mutations found in the fourth transmembrane domain of connexin32. Frameshift and premature stop of translation are supposed to result in a non-functional carboxy-terminus. Two further families had the known missense mutations Arg15Trp and Arg22Gln. Several female carriers were found normal on clinical presentation, however, the genotype was paralleled by decreased nerve conduction velocities (NCV) and slowed central conduction of brain stem auditory evoked responses (BAER). Median motor NCVs showed mild (in women) to intermediate (in males) reduction, indicating a peripheral neuropathy with a predominating axonal component. Nerve biopsy findings were consistent with the electrophysiological data showing a marked loss of large myelinated fibres and clusters of regenerating axons. Electron microscopy revealed various alterations of the axoglial attachment zone. This suggests defective axon-Schwann cell interactions which may induce the axonopathy in CMTX.

Enhancement of K+ conductance improves in vitro the contraction force of skeletal muscle in hypokalemic periodic paralysis

An abnormal ratio between Na+ and K+ conductances seems to be the cause for the depolarization and paralysis of skeletal muscle in primary hypokalemic periodic paralysis. Recently we have shown that the "K+ channel opener" cromakalim hyperpolarizes mammalian skeletal muscle fibers. Now we have studied the effects of this drug on the twitch force of muscle biopsies from normal and diseased human skeletal muscle. Cromakalim had little effect on the twitch force of normal muscle whereas it strongly improved the contraction force of fibers from patients suffering from hypokalemic periodic paralysis. Recordings of intracellular K+ and Cl- activities in human muscle and isolated rat soleus muscle support the view that cromakalim enhances the membrane K+ conductance (gK+). These data indicate that "K+ channel openers" may have a beneficial effect in primary hypokalemic periodic paralysis.

[Prevention of oxaliplatin-induced neuropathy by carbamazepine. A pilot study]

INTRODUCTION

Oxaliplatin has been proven antitumoral activity in numerous clinical trials. Peripheral sensory neuropathy with predominantly hyperpathic symptoms induced by cold is the most severe and dose-limiting toxicity resulting from oxaliplatin therapy. We demonstrated that oxaliplatin alters sodium channel kinetics on sensory neurons. This effect could be antagonized in vitro by the sodium channel blocker carbamazepine. Therefore a pilot study was initiated to investigate if carbamazepine prevents oxaliplatin-induced neuropathy in patients with colorectal cancer.

PATIENTS AND METHODS

Ten patients (six males, four females, mean age 56 +/- 12 years) refractory to 5-fluorouracil were treated with oxaliplatin, 5-fluorouracil, and folinic acid. The patients additionally received carbamazepine. Doses were adapted to a serum level of 3 - 6 mg/l. Patients were questioned about side-effects weekly and treatment-related toxicities were documented using the modified WHO scale. Results were compared with 30 historic controls treated with the same chemotherapy without carbamazepine.

RESULTS

The cumulative oxaliplatin dose was higher in the carbamazepine group (median 722 mg/m(2) and 510 mg/m(2), respectively, p = 0.020). Carbamazepine levels were 4.5 +/- 1.5 mg/l. In contrast to the control group no neuropathy higher than grade 1 occurred in the carbamazepine group. Rate of carbamazepine-induced side effects was low.

CONCLUSIONS

These observations demonstrate that oxaliplatin-induced sensory neuropathy more than grade 1 may be prevented by carbamazepine. Prevention of oxaliplatin-induced neurotoxicity by carbamazepine would possibly enable chemotherapy with considerable higher doses of oxapliplatin and thus enhance activity. A multicenter trial will elucidate if more serious distal neurotoxicities, which occur after application of higher cumulative doses of oxaliplatin, can also be prevented by carbamazepine.

Differences in the sensitivity to purinergic stimulation of myelinating and non-myelinating Schwann cells in peripheral human and rat nerve

Schwann cells of the peripheral nervous system are distinguished by morphological and functional criteria in myelinating and non-myelinating subtypes. We and others have previously reported that Schwann cells in isolated peripheral human and rat nerve respond to extracellular application of ATP with a rise in the intracellular free calcium concentration [Ca2+]i. In the present study, the receptors mediating these Ca2+ transients have been investigated in myelinating and non-myelinating Schwann cells of intact fascicles of isolated human sural nerves, rat ventral roots, and rat vagus nerves. Microfluorometry and confocal laser scanning was used on preparations stained with the Ca2+-sensitive dyes Calcium Green-1 and Fura Red. In myelinating Schwann cells of human and rat nerves, the ATP-induced rise of [Ca2+]i resulted from the activation of a P2Y2 purinoceptor subtype (rank order of potency: UTP > or = ATP >> 2-MeSATP = ADP). In contrast, in non-myelinating Schwann cells, Ca2+ transients were produced by activation of a P2Y1 purinoceptor subtype (rank order of potency: 2-MeSATP > ATP > ADP >> UTP). The P1 agonist adenosine and alpha,alpha-meATP did not evoke Ca2+ signals. Ca2+ transients in both types of Schwann cells were found to be due to Ca2+ release from cyclopiazonic acid-sensitive intracellular stores. However, inhibition by suramin was only found in non-myelinating Schwann cells. These findings indicate that mammalian Schwann cells express phenotype-specific P2Y receptor subtypes.

X-linked dominant Charcot-Marie-Tooth disease: nerve biopsies allow morphological evaluation and detection of connexin32 mutations (Arg15Trp, Arg22Gln)

X-linked Charcot-Marie-Tooth neuropathy (CMTX) is caused by mutations in the connexin32 gene on Xq13. Because of overlapping morphological and clinical data, CMTX patients often meet the criteria of autosomal-dominant CMT2, the neuronal type of CMT. Hence, it might be useful to analyse the connexin32 gene in suspected CMT2 patients when there is no male-to-male transmission. We selected a cohort of 30 patients who were considered having CMT2 on the basis of previous clinical and histopathological evaluation. DNA was extracted from paraffin-embedded sural nerve biopsy samples and screened for connexin32 mutations to verify the possible diagnosis of CMTX. In 2 patients mutations were found corresponding to amino acid substitutions of arginine for tryptophan in codon 15 and arginine for glutamine in codon 22 of connexin32. This study illustrates that archival material allows genetic classification of suspected CMT cases. Furthermore, there is additional proof that connexin32 mutations represent the underlying genetic defect in some cases of predominantly neuronal CMT.

Capsaicin blocks tetrodotoxin-resistant sodium potentials and calcium potentials in unmyelinated C fibres of biopsied human sural nerve in vitro

Topical application of capsaicin has been tested recently for treatment of painful peripheral neuropathy. In the present study, effects of capsaicin were explored on compound action potentials of isolated fascicles from human sural nerve biopsies. Capsaicin reduced the C fibre component by 30-60%; the remaining C fibres were not sensitive to the drug. A good correlation was found between the sensitivity of C fibres to capsaicin and their resistance to tetrodotoxin (TTX), i.e. C fibre action potentials recorded in the presence of TTX were completely blocked by capsaicin. Calcium action potentials seen after inhibition of axonal potassium conductances were also completely suppressed. The data indicate that application of capsaicin nearby human peripheral nerves might prevent action potential conduction in specific subtypes of C fibres.

A special blocker reveals the presence and function of the hyperpolarization-activated cation current IH in peripheral mammalian nerve fibres

Electrotonic responses recorded extra- or intracellularly from peripheral nerve preparations show a "sag" to hyperpolarizing current pulses. The biophysical nature of this "inward rectification" is still under discussion since the phenomenon has not been noted at voltage-clamped single nerve fibres, and since Cs+, which reduces inward rectification, is not a specific ion channel blocker. In this study, we found that low micromolar concentrations of ZD 7288, a specific blocker of the hyperpolarization-activated cationic current (Ih) in the soma of central mammalian neurons, result in a complete block of inward rectification in the electrotonic responses of isolated rat spinal dorsal roots. In addition, ZD 7288 enhanced the activity-dependent slowing of conduction seen in compound C fibre action potentials of isolated rat vagus nerves and augmented the post-tetanic hyperpolarization following trains of action potentials in unmyelinated and myelinated axons. The data suggest that ZD 7288 is a potent blocker and a useful research tool for the study of hyperpolarization-activated inward rectification (Ih) of peripheral nerve preparations.

The role of axonal ion conductances in diabetic neuropathy: a review

Diabetic neuropathy is a common complication in diabetes mellitus. Diabetic neuropathy is accompanied by alterations in axonal excitability, which can lead to either "positive" (paresthesia, dysesthesia, pain) and/or "negative" (hypesthesia, anesthesia) symptoms. The mechanisms underlying these alterations in axonal excitability are not well understood. Clinical tests reveal reduced nerve conduction velocity and axonal loss, but fail to explain nerve excitability. Many different factors have been suggested in relation to the pathophysiology of diabetic neuropathy. There are probably as many factors as there are different clinical pictures in diabetic neuropathy. Nevertheless, it seems that hyperglycemic hypoxia is mainly responsible for the electrophysiological changes seen in damaged diabetic nerves. This article summarizes experimental data indicating that a dysfunction of ion conductances, especially voltage-gated ion channels, could contribute to abnormalities in the generation and/or conduction of action potentials in diabetic neuropathy.

Hyperglycaemic hypoxia alters after-potential and fast K+ conductance of rat axons by cytoplasmic acidification

1. The effects of hyperglycaemic hypoxia (a condition possibly involved in the pathogenesis of diabetic neuropathy) on the depolarizing after-potential and the potassium conductance of myelinated rat spinal root axons were investigated using electrophysiological recordings from intact spinal roots and from excised, inside-out axonal membrane patches. 2. Isolated spinal roots were exposed to hypoxia in solutions containing normal or high glucose concentrations. The depolarizing after-potential of compound action potentials was only enhanced in spinal roots exposed to hyperglycaemic (25 mM D-glucose) hypoxia. A maximal effect was seen in bathing solutions with low buffering power. 3. The depolarizing after-potential was also enhanced by cytoplasmic acidification after replacement of 10-30 mM chloride in the bathing solution by propionate. 4. Multi-channel current recordings from excised, inside-out axonal membrane patches were used to study the effects of cytoplasmic acidification on voltage-dependent K+ conductances with fast (F channels) and intermediate (I channels) kinetics of deactivation. 5. F channels were blocked by small changes in cytoplasmic pH (50% inhibition at pH 6.9). I channels were much less sensitive to intra-axonal acidification. 6. In conclusion, our data show that hyperglycaemic hypoxia enhances the depolarizing after-potential in peripheral rat axons. The underlying mechanism seems to be an inhibition of a fast, voltage-dependent axonal K+ conductance by cytoplasmic acidification. This alteration in membrane conductance may contribute to positive symptoms in diabetic neuropathy.

Two different types of potassium channels in human skeletal muscle activated by potassium channel openers

The inside-out patch clamp technique was used to record the effects of K+ channel openers (EMD 52692, RP 49356 and Cromakalim) on single channel currents in membrane blebs of human skeletal muscle. Two types of K+ channels were activated by these drugs: an ATP-sensitive K+ channel which was inhibited by 3 mM ATP and 5 microM Glibenclamide and an ATP insensitive K+ channel. The open probability of both types was strongly increased by K+ channel openers. Glibenclamide antagonized the action of the K+ channel openers.

K+ channel openers suppress myotonic activity of human skeletal muscle in vitro

Isolated fibre bundles from myotonic human skeletal muscle showed after-contractions and spontaneous mechanical activity. The K+ channel openers cromakalim (10-100 mumols/l) and EMD 52962 (1-10 mumols/l) completely suppressed these abnormalities in mechanical activity. Voltage-clamp experiments revealed that cromakalim (100 mumols/l) increased the membrane K+ conductance of isolated, non-myotonic human skeletal muscle fibres 4-fold; Cl- conductance was not altered. The data show that myotonia is suppressed by an increase in in membrane K+ conductance.

Paclitaxel administered over 3 h followed by cisplatin in patients with advanced head and neck squamous cell carcinoma: a clinical phase I study

We have performed a clinical phase I trial of a combination treatment with paclitaxel given as 3-hour infusion and cisplatin to determine the maximum tolerated dose and the dose-limiting toxicity in patients with recurrent or metastatic squamous cell carcinoma of the head and neck. Treatment was repeated every 21 days. Doses administered ranged from 135 mg/m2 paclitaxel/75 mg/m2 cisplatin to 250 mg/m2 paclitaxel/100 mg/m2 cisplatin. Twenty-four patients have been entered into this study. The maximum tolerated dose was determined to be 225-250 mg/m2 paclitaxel/100 mg/m2 cisplatin. The dose-limiting toxicity of this regimen was myelosuppression (granulocytopenia). Neurosensory and neuromotor toxicity was moderate. However, analyses of threshold electrotonus studies indicated subclinical neurotoxicity in most patients. One patient receiving 200 mg/m2 paclitaxel/100 mg/m2 cisplatin developed grade 3 motor-neurotoxicity. Orthostatic hypotension was observed in 8 patients receiving doses of 200 mg/m2 paclitaxel/100 mg/m2 cisplatin or higher. Objective responses were observed at paclitaxel 175 mg/m2/ cisplatin 100 mg/m2 (n = 5; complete response in 1 patient), paclitaxel 200 mg/ m2/cisplatin 100 mg/m2 (n = 3; partial response in 3 patients) and at paclitaxel 225 mg/m2/cisplatin 100 mg/m2 (n = 8; partial response in 1 patient). Eleven additional patients had stable disease. We conclude that paclitaxel administered as a 3-hour infusion followed by cisplatin is an active regimen in advanced head and neck cancer and that orthostatic hypotension may be a potentially significant clinical toxicity.

High conductance anion channel in Schwann cell vesicles from rat spinal roots

Potassium uptake, possibly together with chloride, is one of the presumed functions of Schwann cells in the peripheral nervous system. However, the presence of chloride channels has not been demonstrated in adult Schwann cells. We present here a new method which allows single channel recordings to be made from Schwann cells in situ without enzymatic treatment. Isolated rat spinal roots were split mechanically into several bundles. Within about 30 min after this procedure small bleb-like vesicles (approximately 20-30 microns in diameter) with a clean surface appeared at the edges of the fibre bundles. Immunofluorescence microscopy with a surface marker for Schwann cell membranes (monoclonal antibody O4) revealed that the vesicles originate from Schwann cells. In standard patch clamp recordings with symmetrical bath and pipette solutions (excised inside-out configuration) an anion channel with the following characteristics was mainly observed: 1) single channel slope conductance of 337 +/- 5 pS in 125 mM KCl and 209 +/- 6 pS in 125 mM K+ methylsulphate; 2) ion permeability ratio: PCl/PK/Pgluconate = 1/0.12/0.06; 3) linear current-voltage relationship (range +/- 60 mV); and 4) voltage- and time-dependent inactivation (the channel was most active at potentials +/- 20 mV). Pharmacologically, the channel was completely blocked with zinc (1 mM) and barium (10 mM). A similar anion channel, showing characteristics 1-4), has been described in cultured Schwann cells of newborn rats (Gray et al., 1984). We now demonstrate that this channel is also present in adult Schwann cells in situ.

Clinical phase II evaluation of paclitaxel in combination with cisplatin in metastatic or recurrent squamous cell carcinoma of the head and neck

BACKGROUND

Paclitaxel as single agent has shown marked activity in several malignancies. The aim of the present phase II trial was to determine the activity of paclitaxel/cisplatin in patients with metastatic or recurrent squamous cell carcinoma of the head and neck.

PATIENTS AND METHODS

200 mg/m2 paclitaxel was administered over three hours followed by cisplatin (100 mg/m2), repeated every 22 days. Twenty-eight patients were entered and received a total of 99 cycles (median 2, range 1-6). All patients were evaluable for toxicity, and 25 for response.

RESULTS

Hematologic toxicities included leukopenia CTC grade 3 in 13 patients, and grade 4 in five patients, neutropenia grade 3 in nine patients, and grade 4 in eight patients, grade 3 anemia and grade 2 thrombocytopenia in one patient each. Non-hematologic toxicities included hypotension grade 2 (six patients), grade 3 (four patients), and grade 4 (two patients). A decline in renal function was observed in 15 courses and 10 patients, leading to a median delay of 2.5 days. Neurosensory and neuromotor toxicity grade 1 were observed in 13 patients (grade 2: 12 patients; grade 3: one patient), myalgia grade 3 in one patient, asthenia grade 3 in two and grade 4 in one patient. Partial responses were observed in 12 patients for an overall response rate of 48% (95% CI: 28%-68%) with a median response duration of 6.5 months (range 1-10 months). Stable disease was observed in seven patients, of who two also had clinical benefit.

CONCLUSIONS

Paclitaxel 200 mg/m2 administered over three hours combined with cisplatin 100 mg/m2 is an active regimen warranting further evaluation.

A mechanosensitive K+ channel with fast-gating kinetics on human axons blocked by gadolinium ions

Current recordings from single mechanosensitive potassium channels were obtained from cell-attached and excised patches of human axons. The channel showed an inwardly rectifying I-V relationship with a slope conductance of 52 pS at negative potentials (symmetrical high potassium solution). The fast-gating kinetics of the channel were best described by one time constant for the open state and two time constants for the closed state. The open probability of this channel increased as negative pressure was applied to the patch pipette. The pressure dependence of the open probability of the mechanosensitive K+ channel followed a sigmoid relationship. Gadolinium (0.5-1 mM) acted as a potent blocker when applied to the intra- and extracellular side of the patch membrane.

[Regional distribution of predisposition to maligant hyperthermia in Germany: tate in 1997]

Malignant hyperthermia (MH) is a rare autosomally dominantly hereditary and potentially life-threatening disease. The prevalence of the genetic MH predisposition is estimated as 1:10,000 to 1:20,000. In Germany no data on the regional distribution are available. Therefore, the purpose of this investigation is to summarise and present the epidemiological data of all German MH laboratories. Nine German hospitals offer the specific in vitro contracture test to diagnose the MH predisposition. All German MH laboratories carry out the examination in accordance with the standardised protocol of the European Malignant Hyperthermia Group. The laboratories were asked to provide the number of all patients investigated, excluding those suffering from other neuromuscular diseases, separated according to diagnostic groups and their places of residence, the number of the identified MH-families as well as the number of the clinically suspected and investigated MH cases with their places of residence. Eight MH laboratories provided the requested data. Until September 1997 a total of 2620 patients were investigated. In 865 patients (34%) MH suspicion was confirmed (diagnosis: MHS). 1494 patients (56%) were released by investigation from MH-suspicion (diagnosis: MHN). In 261 patients (10%) the MH-predisposition remained unsolved (diagnosis: MHE). 580 MH families were identified. Among 2620 patients 757 were clinically suspected MH cases. 35% of these suspected MH cases were classified as MHS, 10% as MHE and 55% as MHN. The documentation of the patients places of residence classified as MHS and MHE into a map of Germany demonstrates an exhaustive distribution with an increased regional prevalence in the areas of the MH laboratories. This concentration in the area of the MH laboratories becomes even more evident, when the places of residence of the MH suspected cases are demonstrated. In conclusion, the distribution of the MH predisposition is uniform and exhaustive in Germany. The presented regional concentration of clinically suspected MH cases among the MH laboratories is mainly interpreted as an expression of effective regional education and information. Considering the overall incidence of the MH predisposition as described above only 15-20% of the MH patients have so far been identified. The MH laboratories have already released about 10,000 patients from the suspicion of MH predisposition. A preliminary prevalence of at least 1:60,000 to 1:80,000 in Germany can be estimated according to the presented data.

Sodium channel inactivation kinetics of rat sensory and motor nerve fibres and their modulation by glutathione

Na+ channel currents of rat motor and sensory nerve fibres were studied with the patch-clamp technique on enzymatically demyelinated axons. Differences between motor and sensory fibres in multi-channel inactivation kinetics and the gating of late single-channel currents were investigated. In the axon-attached mode, inactivation of multi-channel Na+ currents in sensory axons was best fitted with a single time constant while for motor axons two time constants were needed. Late single-channel currents in sensory axons were characterized by short openings whereas motor axons exhibited additional long single-channel openings. In contrast, in excised, inside-out membrane patches, no differences between motor and sensory fibres were found; in both types of fibre inactivation of multi-channel Na+ currents proceeded with two time constants and late single-channel currents showed short and long openings. After application of the reducing agent glutathione to the cytoplasmic side of excised inside-out patches, inactivation of Na+ currents in both motor and sensory fibres proceeded with a single, fast exponential time constant and late currents appeared with short openings only. These data indicate that the axonal metabolism may contribute to the different inactivation kinetics of Na+ current in motor and sensory nerve fibres.

Glutathione accelerates sodium channel inactivation in excised rat axonal membrane patches

The effects of glutathione were studied on the gating behaviour of sodium channels in membrane patches of rat axons. Depolarizing pulses from -120 to -40 mV elicited sodium currents of up to 500 pA, indicating the simultaneous activation of up to 250 sodium channels. Inactivation of these channels in the excised, inside-out configuration was fitted by two time constants (tau h1 = 0.81 ms; tau h2 = 5.03 ms) and open time histograms at 0 mV revealed a biexponential distribution of channel openings (tau short = 0.28 ms; tau long = 3.68 ms). Both, the slow time constant of inactivation and the long lasting single channel openings disappeared after addition of the reducing agent glutathione (2-5 mM) to the bathing solution. Sodium channels of excised patches with glutathione present on the cytoplasmatic face of the membrane had inactivation kinetics similar to channels recorded in the cell-attached configuration. These observations indicate that redox processes may contribute to the gating of axonal sodium channels.

Secondary myopathy due to systemic diseases

Background

Some systemic diseases also affect the skeletal muscle to various degrees and with different manifestations. This review aimed at summarizing and discussing recent advances concerning the management of muscle disease in systemic diseases.

Method

Literature review by search of MEDLINE, and Current Contents with appropriate search terms.

Results

Secondary muscle disease occurs in infectious disease, endocrine disorders, metabolic disorders, immunological disease, vascular diseases, hematological disorders, and malignancies. Muscle manifestations in these categories include pathogen‐caused myositis, muscle infarction, rhabdomyolysis, myasthenia, immune‐mediated myositis, necrotising myopathy, or vasculitis‐associated myopathy. Muscle affection may concern only a single muscle, a group of muscles, or the entire musculature. Severity of muscle affection may be transient or permanent, may be a minor part of or may dominate the clinical picture, or may be mild or severe, requiring invasive measures including artificial ventilation if the respiratory muscles are additionally involved. Diagnostic work‐up is similar to that of primary myopathies by application of non‐invasive and invasive techniques. Treatment of muscle involvement in systemic diseases is based on elimination of the underlying cause and supportive measures. The prognosis is usually fair if the causative disorder is effectively treatable but can be fatal in single cases if the entire musculature including the respiratory muscles is involved, in case of infection, or in case of severe rhabdomyolysis.

Conclusion

Secondary muscle manifestations of systemic diseases must be addressed and appropriately managed. Prognosis of secondary muscle disease in systemic diseases is usually fair if the underlying condition is accessible to treatment.