Pharmacology of the putative M₄ muscarinic receptor mediating Ca‐current inhibition in neuroblastoma × glioma hybrid (NG 108–15) cells

Abstract

1 We have assessed the potency of a range of agonists and antagonists on the muscarinic receptor responsible for inhibiting the Ca-current (ICa) in NG 108-15 hybrid cells.2 Acetylcholine (ACh), oxotremorine-M and carbachol were potent 'full' agonists (EC50 values were 0.11 M, 0.14 fM and 2pM, respectively). Maximum inhibition of peak high-threshold ICa by these agonists was 39.5%. (±)-Muscarine, methylfurmethide and arecaidine propargyl ester (APE) were 'partial' agonists, with EC50 values of 0.54 pM, 0.84pm and 0.1 pm, respectively. 3 Atropine, pirenzepine and himbacine were potent antagonists of muscarinic inhibition of ICa, with apparent pKB values of 9.8, 7.74 and 8.83, respectively. Methoctramine was relatively weak (pKB = 7.63). Atropine and pirenzepine depressed maximum responses to agonists, probably because these antagonists have relatively slow dissociation rates. 4 The characteristic pharmacological profile found for the M4 receptors in these functional experiments (himbacine high affinity, pirenzepine moderate to high affinity, methoctramine low affinity) corresponds well with data from earlier binding experiments (Lazareno et al., 1990). Since mRNA hybridising to probes for the m4 receptor genotype can be detected in these cells, it is suggested that these pharmacological characteristics identify the equivalent expressed receptor subtype M4.

Characterization of muscarinic receptors mediating contractions of circular and longitudinal muscle of human isolated colon

“…In our study the pA2 values for CM (7.47) and LM (7.54) were within the range (6.9-7.6) noted for its actions at a range of purported M3 receptors (Caulfield, 1993;Eglen et al, 1994). Moreover, our pA2 values were less than that observed for himbacine at the M4 muscarinic receptor of NG108-15 cells, 8.83 (Caulfield & Brown, 1991), the MI muscarinic receptor of the rat vas deferens, 8.64 (Eltze & Figala, 1988) and the M2 muscarinic receptor of the rat heart, 8.34 (Lazareno et al, 1990).…”

“…Himbacine exhibits an affinity profile M2 > M4 > M1 > M3 (Lazareno et al, 1990;Caulfield & Brown, 1991;Russo et al, 1993). In our study the pA2 values for CM (7.47) and LM (7.54) were within the range (6.9-7.6) noted for its actions at a range of purported M3 receptors (Caulfield, 1993;Eglen et al, 1994).…”

“…HHSiD and p-F-HHSiD have a relatively higher affinity for M3 muscarinic receptors than M2 muscarinic receptors but do have affinity for Ml and M4 muscarinic receptors (Lambrecht et al, 1989;Waelbroeck et al, 1990). Himbacine has relatively high affinity for M2 and M4 muscarinic receptors with lower affinity for Ml and M3 muscarinic receptors (Eglen et al, 1988;Caulfield & Brown, 1991;Miller et al, 1992;Russo et al, 1993).…”

“…In the published literature, atropine has been used as a non-selective high affinity antagonist at muscarinic receptors. Pirenzepine is a relatively high affinity antagonist for Ml muscarinic receptors with intermediate affinity for M4 muscarinic receptors and lower affinity for the M2 and M3 muscarinic receptors (Lambrecht et al, 1989;Caulfield & Brown, 1991;Dorje et al, 1991;Grimm et al, 1994). (11-[[[2 -(diethylamino)methyl] -l-piperidinyl]acetyl] -5,1 1-dihydro-6H-pyridol [2,3,-b][1,4]benzodiazepine-6-one) has high affinity for the M2 muscarinic receptor, but also has affinity for the Ml muscarinic receptor with lower affinity for the M3 and M4 muscarinic receptors (Birdsall & Hulme, 1983;Giachetti et al, 1986;Hammer et al, 1986).…”

Characterization of muscarinic receptors mediating vasodilation in guinea-pig ileum submucosal arterioles by the use of computer-assisted videomicroscopy

“…There is a candidate M 4 receptor, found in rat striatum (Waelbroeck et al,1 990). rabbit Jung (Lazareno et al, 1990) and NG108-l5 cells (Michel et al, 1989;Caulfield and Brown, 1991), which is considered to be the m4 gene product (Dörje et al, 199la;Brann et al, 1988).…”