A MUSCARINIC ACETYLCHOLINE-RECEPTOR, PRESENT IN THE EPITHELIAL-CELL LINE FROM CHIRONOMUS-TENTANS

A muscarinic cholinergic receptor (mAchR) is present in the non-neuron al epithelial cell line from Chironomus tentans. Scatchard plot analys is (K-D = 1.4 nM) using the non-selective antagonist quinuclidinylbenz ilate (QNB), as well as kinetic data (K-D = 1.7 nM), reveals one class of high affinity binding sites. About 2000 binding sites/cell are pre sent. The receptor concentration (54.5 +/- 7.5 fmol/mg protein) is com parable to the values reported from insect brain. The receptor interac ts only with muscarinic ligands; nicotinergic acetylcholine receptors are not present, Binding properties are not comparable to any of the m uscarinic subtypes known from vertebrate tissues. The rank order of co mpetition of radiolabeled QNB is: QNB > atropine > PrBCM > oxotremorin e, pirenzepine > methoctramine, The competition curve obtained with ca rbamylcholine is shifted to higher ligand concentrations in the presen ce of Gpp(NH)p and to lower carbamylcholine concentrations by 1 mM NEM , With antibodies against muscarinic receptor from calf brain one band with a molecular weight of about 80 kDa is detected on Western blots, The moulting hormone 20-OH-ecdysone transiently increases the concent ration of muscarinic receptor.