Neuromuscular - Neuro-muscular disorders and the...

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Neuro-muscular disorders and the Acetylcholine receptor Joseph M. Caiati, MD Department of Anesthesiology
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Overview The Neuromuscular Junction Diseases that Increase AChRs in Skeletal Muscle Disease that decreases AChRs in Skeletal Muscle Succinylcholine and other NDMRs Sugammadex
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The Neuromuscular Junction Normal AChRs at NMJ are nicotinic AChRs only in Neuromuscular Junction 75% blocked=weakness 95%=paralysis Depolarization with SCh leads to increase in serum K+ of 0.5-1.0meq/L ACh and SCh act briefly at NMJ due to rapid metabolism by ACh esterase
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Normal
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Classic receptor theory Lack of receptor stimulation causes receptor proliferation Heavy receptor stimulation causes receptor number to decrease If there is a proliferation of AChRs There will be increased sensitivity to agonists (SCh) There will be decreased sensitivity to competitive antagonists (NDMR)
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The Neuro-Muscular Junction up-regulated AChRs spread throughout the muscle membrane - up to 100X more receptors Additional Isoforms of AChRs expressed when lack of NM transmission Metabolites of ACh and SCh (choline) will also strongly and persistently open (2-10X) the AChRs exaggerating the K+ flow
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The Neuro-Muscular Junction up-regulated ACh from nerve terminal in upregulated state does not cause hyperkalemia- ACh esterase prevents spread beyond NMJ Systemic SCh reaches all AChRs and depolarizes all virtually simultaneously many far from ACh esterase of nerve terminal- metabolites as well continue to open channels causing hyperkalemia
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Pharmacologic Basis for Agonist (SCh) Sensitivity Upregulated AChRs stay open longer in response to agonist Metabolites of both ACh and SCh (choline) also can open the upregulated (immature) AChRs
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Pharmacologic Basis for Resistance to NDMRs More AChRs- upregulation Same amount of NDMR ACh can still find many available AChRs to cause depolarization and muscle twitch
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AChRs in Skeletal Muscle a.k.a “ up-regulation
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This note was uploaded on 12/28/2011 for the course STEP 1 taught by Professor Dr.aslam during the Fall '11 term at Montgomery College.

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Neuromuscular - Neuro-muscular disorders and the...

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