FIve distinct but related muscarinic receptors had been identified. These glycosylated proteins have single chains of 460 to 590 amino acids that
are thought to span the plasma membrane 7 times, creating 4 extracellular domains, 7 helical hydrophobic
transmembrane domains, and 4 intracellular domains. Each protein is the product of a different gene without introns in
the coding sequence, and the amino acid sequences in the receptor subtypes are remarkably homologous among different
animal species.
NCBI Summary:
The muscarinic cholinergic receptors belong to a larger family of G protein-coupled receptors. The functional diversity of these receptors is defined by the binding of acetylcholine to these receptors and includes cellular responses such as adenylate cyclase inhibition, phosphoinositide degeneration, and postassium channel mediation. Muscarinic receptors influence many effects of acetylcholine in the central and peripheral nervous system. The muscarinic cholinergic receptor 3 controls smooth muscle contraction and its stimulation causes secretion of glandular tissue.
General function
Receptor
Comment
Cellular localization
Plasma membrane
Comment
Ovarian function
Oogenesis
Comment
Arellano RO, et al reported that muscarinic receptor heterogeneity in follicle-enclosed Xenopus
oocytes.
Ionic current responses elicited by acetylcholine (ACh) in follicle-enclosed
Xenopus oocytes (follicles) were studied using the two-electrode voltage-clamp
technique. ACh generated a fast chloride current (Fin) and inhibited K+ currents
gated by cAMP (IK,cAMP) following receptor activation by adenosine,
follicle-stimulating hormone or noradrenaline. These previously described
cholinergic responses were confirmed to be of the muscarinic type, and were
independently generated among follicles from different frogs. Using reverse transcription-PCR, transcripts of a previously cloned
muscarinic receptor from Xenopus (XlmR) were amplified from the RNA of both
the isolated follicular cells and the oocyte. The pharmacological and molecular
characteristics suggest that XlmR is involved in IK,cAMP inhibition. . In
conclusion, follicular cells possess two different muscarinic receptors, one
resembling the M2 (or M4) subtype and the other the M3 subtype. These receptors
are coupled to distinct membrane mechanisms leading to independent regulation of
two membrane conductances.
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
Fritz S, et al 2001 reported the expression of muscarinic receptor types in the primate ovary
and evidence for nonneuronal acetylcholine synthesis.
Because luteinized human granulosa cells (GC) in culture express
functional MR, the authors have determined whether the group of the related MR
subtypes, M1R, M3R, and M5R, are present in vivo in human and rhesus monkey
ovaries. To this end, ribonucleic acids (RNAs) of different human and monkey
ovaries as well as RNAs from human GC and monkey oocytes were reverse
transcribed and subjected to PCR amplification, followed by sequencing of the
amplified complementary DNAs. Results obtained showed that M1R, M3R, and M5R
messenger RNAs are present in adult human and monkey ovaries; oocytes express
exclusively the M3R subtype, whereas GC express M1R and M5R.