Study note
PharmacologyCHOLINERGIC TRANSMISSION & CHOLINERGIC DRUGS

Cardiac M2 signalling and nicotinic receptor subtypes

THE CONTEXT
This passage completes cardiac muscarinic signalling and describes the structure, locations and selective pharmacology of nicotinic receptors.

Cardiac muscarinic signalling

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M2 signalling involves potassium-channel opening through Gi and inhibition of adenylyl cyclase.
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The resulting cardiac effects include hyperpolarization, reduced pacemaker activity, slower conduction and decreased force of contraction.

Nicotinic receptor mechanism

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Nicotinic receptors are selectively activated by nicotine and blocked by tubocurarine or hexamethonium.
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They are rosette-like pentameric structures enclosing a ligand-gated cation channel.
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Activation opens the channel, allowing rapid cation flow that produces depolarization and an action potential.

NM receptors

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NM receptors occur at skeletal muscle endplates and mediate skeletal muscle contraction.
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They are selectively stimulated by phenyl trimethyl ammonium, abbreviated PTMA, and blocked by tubocurarine.

NN receptors

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NN receptors occur on sympathetic and parasympathetic ganglionic cells, adrenal medullary cells, and in the spinal cord and certain brain regions.
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They are selectively stimulated by dimethyl phenyl piperazinium, abbreviated DMPP, and blocked by hexamethonium.
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NN receptors constitute the primary pathway of transmission in autonomic ganglia.
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