Journal of Neuroscience, Vol 11, 3763-3771, Copyright © 1991 by Society for Neuroscience
The molecular and pharmacological properties of muscarinic cholinergic receptors expressed by rat sweat glands are unaltered by denervation
MP Grant, SC Landis and RE Siegel
Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106.
Previous studies have indicated that denervation of adult rodent sweat
glands results in the loss of secretory responsiveness to muscarinic
agonists. To elucidate the molecular basis of this loss, we have
characterized the muscarinic cholinergic receptor present in adult rat
sweat glands and examined the effects of cholinergic denervation on its
properties and expression. When homogenates of gland-rich tissue from adult
animals were assayed with [N-methyl-3H]-scopolamine, a high- affinity
muscarinic antagonist, the concentration of muscarinic receptors was 301
fmol/mg protein and the affinity was 131 pM. Autoradiographic analysis
demonstrated that ligand binding sites were detectable only on glands. In
competition studies with well- characterized muscarinic agents, the
receptor exhibited typical muscarinic pharmacology. Further investigation
with the selective muscarinic antagonists
4-diphenylacetoxy-N-methylpiperidine methiodide, pirenzepine, and AF DX-116
revealed that the sweat gland receptor belongs to the M2 glandular
pharmacological subtype. In situ hybridization histochemistry with receptor
subtype-specific oligonucleotide probes indicated that rat sweat glands
express the m3 molecular receptor subtype. Seven days after sciatic nerve
transection, when denervated glands were compared to those on the
contralateral unoperated side, there was no significant difference either
in the concentration or affinity of muscarinic binding sites or in receptor
density or distribution. Furthermore, the molecular subtype and the level
of its expression were unchanged. Thus, it appears that muscarinic binding
sites and m3 receptor mRNA are present in denervated sweat glands that are
unresponsive to muscarinic stimulation. These results suggest that the
regulation of responsiveness occurs at a point distal to the expression of
muscarinic receptors.
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