CHAPTER 3. DRUGS AFFECTING CHOLINERGIC SYNAPSES

In this Chapter:

3.1. Drugs affecting muscarinic (M) and nicotinic (N) cholinoceptors

3.1.1. Drugs stimulating M- and N-cholinoceptors (M-, N-cholinomimetics)

3.1.2. Drugs blocking M- and N-cholinoceptors (M-, N-cholinoblockers)

3.2. Anticholinesterase drugs

3.3. Drugs affecting muscarinic cholinoceptors

3.3.1. Drugs stimulating M-cholinoceptors (M-cholinomimetics, or muscarinomimetics)

3.3.2. Drugs blocking M-cholinoceptors (M-cholinoblockers, or atropine-like drugs)

3.4. Drugs affecting nicotinic cholinoceptors

3.4.1. Drugs stimulating nicotinic cholinoceptors (N-cholinomimetics)

3.4.2. Blockers of nicotinic cholinoceptors and/or coupled with them ion channels

In cholinergic synapses transmission is mediated by acetylcholine. Acetylcholine is synthesised in the cytoplasm of cholinergic neuron terminals. It is produced from choline and acetyl coenzyme A (of mitochondrial origin) with the participation of cytoplasmic cholinacetylase enzyme (choline acetyltransferase). Acetylcholine is deposited in synaptic vesicles. Each of these contains several thousands of acetylcholine molecules. Nerve impulses cause acetylcholine to release into the synaptic gap, after which it interacts with cholinoceptors.

The structure of cholinoceptors is not fully established. According to current data, cholinoceptors of the neuromuscular synapses consist of five protein subunits (α, α, β, γ, δ) that surround an ion (sodium) channel and pass through the entire thickness of the lipid membrane. Acetylcholine interacts with the α-subunits (Fig. 3.1), and this results in the opening of the ion channel and depolarization of the postsynaptic membrane.

Fig. 3.1. Localization of acetylcholine action on the model of nicotinic cholinoceptor. α-, β-, γ-, and δ-subunits of N-cholinoceptor.