Muscarinic gene products

Four muscarinic receptor subtypes (Mj - M4) have been defined by pharmacological studies. On the other hand, receptor cloning studies revealed the existence of five different but highly homologous muscarinic receptor gene products (ml - m5). 

If a single gene is cloned in sufficient quantity, it can be sequenced (see Deoxyribonucleic acid) and the amino acid sequence of the gene product can be predicted from the nucleotide sequence of the DNA. For example, the amino acid sequences of the insulin receptor, nicotinic and muscarinic cholinergic acetylcholine receptors, epidermal growth factor precursor and many (thousands) other proteins have been predicted in this way. 

Nicotinic and muscarinic effects are mediated by nicotinic and muscarinic receptors, respectively. These receptors are the products of two distinct gene super-families, and their only common prc eity is that bey are activated by A. The slower muscarinic receptor response operates via G-protein-coupled receptors (see G-proteins). Depending on the receptor subtype, the suteequent effector mechanism involves inhibition of adenylate cyclase, formation of inositol 1,4,5-(ruphosphate from phosphoinositides by a specific phospholipase C, or modulation (opening) of certain K channels [D. Brown Nature 319 (1986) 358-359]. 

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