Störungsstelle Ca2+ Kanäle - engl.





Michael T. Flink¹ and William D. Atchison¹–²

Ca²+ Channels as Targets of Neurological Disease:
Lambert-Eaton Syndrome and other Ca²+ Chanellopathies.

Journal of Bioenergetics and Biomembranes,Vol. 35, No. 6, Dec. 2003 (© 2003).

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In the nervous system, voltage-gated Ca²+ channels regulate numerous processes critical to neuronal function including secretion of neurotransmitters, initiation of action potentials in dendritic regions of some neurons, growth cone elongation, and gene expression. Because of the critical role which Ca²+ channels play in signaling processes within the nervous system, disruption of their function will lead to profound disturbances in neuronal function. Voltage-gated Ca²+ channels are the targets of several relatively rare neurological or neuromuscular diseases resulting from spontaneously-occurring mutations in genes encoding for parts of the channel proteins, or from autoimmune attack on the channel protein responses. Mutations in CACNA1A, which encodes for the alpha1A subunit of P/Q-type Ca²+ channels, lead to symptoms seen in familial hemiplegic migraine, episodic ataxia type 2, and spinocerebellar ataxia type 6. Conversely, autoimmune attack on Ca²+ channels at motor axon terminals causes peripheral cholinergic nerve dysfunction observed in Lambert–Eaton Myasthenic Syndrome (LEMS), the best studied of the disorders targeting voltage-gated Ca²+ channels. LEMS is characterized by decreased evoked quantal release of acetylcholine (ACh) and disruption of the presynaptic active zones, the sites at which ACh is thought to be released. LEMS is generally believed to be due to circulating antibodies directed specifically at the Ca²+ channels located at or near the active zone of motor nerve terminals (P/Q-type) and hence involved in the release of ACh. However, other presynaptic proteins have also been postulated to be targets of the autoantibodies. LEMS has a high degree of coincidence (ca. 60%) with small cell lung cancer; the remaining 40% of patients with LEMS have no detectable tumor. Diagnosis of LEMS relies on characteristic patterns of electromyographic changes; these changes are observable at neuromuscular junctions of muscle biopsies from patients with LEMS. In the majority of LEMS patients, those having detectable tumor, the disease is thought to occur as a result of immune response directed initially against voltage-gated Ca²+ channels found on the lung tumor cells. In these patients, effective treatment of the underlying tumor generally causes marked improvement of the symptoms of LEMS as well. Animal models of LEMS can be generated by chronic administration of plasma, serum or immunoglobulin G to mice. These models have helped dramatically in our understanding of the pathogenesis of LEMS. "This passive transfer“ model mimics the electrophysiological and ultrastructural findings seen in muscle biopsies of patients with LEMS. In this model, we have shown that the reduction in amplitude of Ca²+ currents through P/Q-type channels is followed by unmasking of an L-type Ca²+ current not normally found at the motor nerve terminal which participates in release of ACh from terminals of mice treated with plasma from patients with LEMS. It is unclear what mechanisms underlie the development of this novel L-type Ca²+ current involved in release of ACh at motor nerve terminals during passive transfer of LEMS.


KEY WORDS: Lambert–Eaton syndrome; myasthenic syndromes; motor nerve terminal; neuromuscular junction; neuromuscular diseases; Ca channelopathy; acetylcholine release; dihydropyridine; neuromuscular transmission.


1 Department of Pharmacology and Toxicology, Michigan State University, East Lansing, Michigan.
2 To whom correspondence should be addressed at Department of Pharmacology and Toxicology,


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