tetrodotoxin and Muscular-Diseases

Crystalline botulinum toxin type A was licensed in December 1989 by the Food and Drug Administration for treatment of certain spasmodic muscle disorders following 10 or more years of experimental treatment on human volunteers. Botulinum toxin exerts its action on a muscle indirectly by blocking the release of the neurotransmitter acetylcholine at the nerve ending, resulting in reduced muscle activity or paralysis. The injection of only nanogram quantities (1 ng = 30 mouse 50% lethal doses [U]) of the toxin into a spastic muscle is required to bring about the desired muscle control. The type A toxin produced in anaerobic culture and purified in crystalline form has a specific toxicity in mice of 3 x 10(7) U/mg. The crystalline toxin is a high-molecular-weight protein of 900,000 Mr and is composed of two molecules of neurotoxin (ca. 150,000 Mr) noncovalently bound to nontoxic proteins that play an important role in the stability of the toxic unit and its effective toxicity. Because the toxin is administered by injection directly into neuromuscular tissue, the methods of culturing and purification are vital. Its chemical, physical, and biological properties as applied to its use in medicine are described. Dilution and drying of the toxin for dispensing causes some detoxification, and the mouse assay is the only means of evaluation for human treatment. Other microbial neurotoxins may have uses in medicine; these include serotypes of botulinum toxins and tetanus toxin. Certain neurotoxins produced by dinoflagellates, including saxitoxin and tetrodotoxin, cause muscle paralysis through their effect on the action potential at the voltage-gated sodium channel. Saxitoxin used with anaesthetics lengthens the effect of the anaesthetic and may enhance the effectiveness of other medical drugs. Combining toxins with drugs could increase their effectiveness in treatment of human disease.

Topics: Bacterial Toxins; Botulinum Toxins; Humans; Muscular Diseases; Neurotoxins; Saxitoxin; Tetrodotoxin; Virulence Factors, Bordetella

Critical illness myopathy is a disorder in which skeletal muscle becomes electrically inexcitable. We previously demonstrated that a shift in the voltage dependence of fast inactivation of sodium currents contributes to inexcitability of affected fibres in an animal model of critical illness myopathy in which denervated rat skeletal muscle is treated with corticosteroids (steroid-denervated; SD). In the current study we examined whether expression of Nav1.5 contributes to the altered voltage dependence of sodium channel inactivation in SD muscle. We used TTX and mu-conotoxin GIIIB to selectively block Nav1.4 in SD muscle and found that the level of Nav1.5 did not correlate closely with the shift in fast inactivation. Surprisingly, we found that the voltage dependence of inactivation of Nav1.4 was similar to that of Nav1.5 in skeletal muscle in vivo. In severely affected fibres, inactivation of both Nav1.4 and Nav1.5 was shifted towards hyperpolarized potentials. We examined the role of denervation and steroid treatment in the shift of the voltage dependence of inactivation and found that both denervation and steroid treatment contribute to the shift in inactivation. Our results suggest that modulation of the voltage dependence of inactivation of both Nav1.4 and Nav1.5 in vivo contributes to loss of electrical excitability in SD muscle.

Topics: Adrenal Cortex Hormones; Animals; Disease Models, Animal; Muscle Denervation; Muscle Proteins; Muscular Diseases; NAV1.4 Voltage-Gated Sodium Channel; NAV1.5 Voltage-Gated Sodium Channel; Rats; Sodium Channel Blockers; Sodium Channels; Tetrodotoxin

We investigated whether veratrine (5 microl, 10 ng/kg) injected into the mouse extensor digitorum longus (EDL) (fast-twitch) and soleus (SOL) (slow-twitch) muscles provokes distinctive ultrastructural disturbances 15, 30 and 60 min later. The mitochondria in SOL were affected earlier (within 15 min) than in EDL. Swelling of the sarcoplasmic reticulum terminal cisternae was more marked in EDL than in SOL and caused distortion of sarcomeres so that fragmentation of myofilaments was more pronounced in EDL. Hypercontracted sarcomeres were seen mainly in SOL and veratrine caused infoldings of the sarcolemma only in this muscle. In both muscles, the T-tubules remained unaffected and by 60 min after veratrine most of the above alterations had reverted to normal. Pretreatment with tetrodotoxin prevented the alterations induced by veratrine. This suggests that most of the alterations resulted from the enhanced influx of Na+ into muscle fibers. These results emphasize the importance of considering the type of muscle when studying the action of myotoxic agents.

Topics: Animals; Drug Antagonism; Male; Mice; Mice, Inbred BALB C; Mitochondria; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscle, Skeletal; Muscular Diseases; Sarcomeres; Tetrodotoxin; Veratrine

The myotoxicity of pyridostigmine bromide was investigated on rat diaphragm nerve-muscle preparations in vitro. Within 2 h of exposure to pyridostigmine (2 microM), diaphragm muscles exhibited ultrastructural alterations characterized by swelling of subjunctional mitochondria and disorganization of contractile proteins. These alterations developed both in the absence and presence of electrical stimulation of the phrenic nerve, and were accompanied by continuous muscle fasciculations. Pretreatment by tetrodotoxin suppressed both the muscle fasciculations and the appearance of myopathies. These findings suggest that fasciculations may be an important contributing factor in the development of anti-cholinesterase-induced myopathies.

Topics: Acetylcholinesterase; Animals; Diaphragm; Electric Stimulation; Electrophysiology; Male; Microscopy, Electron; Motor Endplate; Muscles; Muscular Diseases; Pyridostigmine Bromide; Rats; Synapses; Tetrodotoxin

Topics: Animals; Cells, Cultured; Disease Models, Animal; Mice; Mice, Mutant Strains; Microscopy, Electron; Muscles; Muscular Diseases; Tetrodotoxin

Dysgenic (mdg/mdg) skeletal muscle of the mouse, grown in primary cell culture, fires action potentials in the absence of contractions, thus allowing analysis of the role of electrical activity (without contraction) on the specific activity and molecular forms of acetylcholinesterase (AChE). Specific activity of AChE was assessed by the spectrophometric method of Ellman (Biochem. Pharmacol., 7 (1961) 88-95) and found to increase by 2-5 times in the active myotubes (contraction and action potentials in normal and action potentials, alone in dysgenic muscle) compared to quiescent muscle. Sucrose density sedimentation analysis of muscle homogenates revealed an increase, by 2-3 times, in the proportion of the asymmetric (16S) molecular form of AChE in active muscle of both genotypes. Thus, electrical membrane activity, and not contraction per se, is directly involved in the regulation of levels of specific activity of and accumulation of the asymmetric (16S) form of AChE in muscle cells in culture.

Topics: Acetylcholinesterase; Action Potentials; Animals; Cells, Cultured; Isoenzymes; Mice; Mice, Mutant Strains; Muscle Contraction; Muscles; Muscular Diseases; Potassium; Tetrodotoxin