Antimuscarinic activity of telenzepine on isolated human urinary bladder: no role for M1-muscarinic receptors

M1 receptor-mediated nitric oxide-dependent relaxation unmasked in stomach fundus from M3 receptor knockout mice

Muscarinic receptors can mediate both contractile and relaxant responses in smooth muscle. The stomach fundus from wild-type mice possesses a neuronal M(1) receptor that mediates relaxation to carbamylcholine and (4-hydroxy-2-butynyl)-1-trimethylammonium-3-chlorocarbanilate chloride (McN-A-343) but is masked by M(3) receptor-mediated contraction to both agonists. When the M(3) receptor was deleted, cholinergic-induced relaxation was unmasked. M(1) receptor antagonism with pirenzepine, nitric oxide (NO) synthase inhibition with N(omega)-nitro-L-arginine methyl ester hydrochloride, and inhibition of neuronal activation with tetrodotoxin abolished relaxation to McN-A-343 in tissues from M(3) receptor knockout mice, supporting the neuronal localization of an M(1) receptor that activated NO release to effect relaxation. However, the cyclooxygenase inhibitor indomethacin did not affect contraction or relaxation to carbamylcholine in stomach fundus from wild-type or M(3) receptor knockout mice, indicating that cyclooxygenase products played no role in these responses. The neuronal M(1) receptor modulated relaxation induced by carbamylcholine and McN-A-343 but not relaxation induced by electric field stimulation of the stomach fundus. These data support the presence of M(1) receptor-mediated relaxation in the stomach and suggest that when the M(3) receptor is eliminated or blocked, M(1) receptor-mediated gastric relaxation may be enhanced, possibly leading to alterations in gastric emptying and subsequent effects on body weight.

Actions of the new antimuscarinic compound Lu 25-109 on isolated human and pig detrusor

The aim of this study was to evaluate the effects of a novel antimuscarinic agent, Lu 25-109, a partial M1 receptor agonist, and M2/M3 receptor antagonist in human and pig detrusor to establish its affinity for muscarinic receptors in human detrusor and parotid gland and to compare the results with those obtained with oxybutynin. Effects on the detrusor were determined as regards the ability to inhibit carbachol-induced contractions and contractions induced by electrical field stimulation (EFS). Radioligand binding studies were performed to assess the ability to displace quinuclidinyl benzilate (3H-QNB) from muscarinic receptors in the detrusor and parotid gland. Lu 25-109 produced a concentration-dependent rightward shift of the concentration-response curves for carbachol in both human and pig detrusor, the pK(b) values being 6.2+/-0.1 (n=6) and 5.8+/-0.3 (n=6). Corresponding values for oxybutynin were 7.9+/-0.1 (n=7) and 7.8+/-0.1 (n=6). Contractions induced by EFS in human detrusor were almost completely inhibited by 100 micromol/L Lu 25-109 (84+/-4%; n=4). In contrast, EFS-induced contractions in pig detrusor were less sensitive to Lu 25-109, resulting in a final inhibition of 32+/-6% (n=9) with the highest concentration used (100 micromol/L). This difference in effect between human and pig detrusor was not observed with oxybutynin. Radioligand binding experiments demonstrated a small difference in affinity for Lu 25-109 in the parotid gland compared with the bladder, the pKi values being 6.2+/-0.1 versus 6.5+/-0.1 (n=4). Corresponding values for oxybutynin were 8.5+/-0.1 versus 8.2+/-0.1 (n=4). The results show that Lu 25-109 competitively and effectively antagonizes carbachol-induced contractions and contractions induced by EFS in human detrusor muscle. Even if Lu 25-109 were less potent than oxybutynin, it has an effect profile that makes it of interest to test its ability to counteract bladder overactivity in humans.

Identification of muscarinic receptor subtypes of cultured smooth muscle cells and tissue of human bladder body

BACKGROUND

Muscarinic receptor subtypes of cultured smooth muscle cells from the human bladder body were investigated by the receptor binding assay method. The result was compared with that obtained from the human bladder body tissue to confirm whether the receptor subtypes of the cells are not changed after several passages of cell culture.

METHODS

Inhibitory effects of various muscarinic antagonists on the binding of [3H]-N-methylscopolamine ([3H]-NMS) to membrane preparations obtained from cultured smooth muscle cells from the fourth subculture of the human bladder body were compared with those prepared from the human bladder body tissue and cells expressing human muscarinic receptor subtypes.

RESULTS

Binding-inhibition constants (pKi) for atropine, pirenzepine, methoctramine, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), oxybutynin and propiverine obtained from membrane preparations of cultured smooth muscle cells were 8.91, 6.35, 8.24, 8.53, 7.29 and 5.61, respectively. pKi values of these muscarinic receptor antagonists against the membrane preparation of human bladder body tissue were 9.08, 6.66, 8.05, 8.79, 7.53 and 6.04, respectively. pKi values of cultured smooth muscle cells and tissue from human bladder body were correlated closely with those of insect cells expressing the cloned human M2 receptor subtype.

CONCLUSION

The binding affinities for various muscarinic receptor antagonists of cultured human smooth muscle cells were maintained through the fourth subculture and it was suggested that the M2 receptor subtype is predominantly expressed in cultured smooth muscle cells of human bladder body as well as in tissue of the human bladder body.

Prejunctional muscarinic inhibitory control of acetylcholine release in the human isolated detrusor: involvement of the M4 receptor subtype

1. Experiments were carried out in human detrusor strips to characterize muscarinic receptor subtypes involved in the prejunctional regulation of acetylcholine (ACh) release from cholinergic nerve terminals, and in the postjunctional smooth muscle contractile response. 2. In detrusor strips preincubated with [3H]-choline, electrical field stimulation (600 pulses) delivered in six trains at 10 Hz produced a tritium outflow and a contractile response. In the presence of 10 microM paraoxon (to prevent ACh degradation) the tritium outflow was characterized by HPLC analysis as [3H]-ACh (76%) and [3H]-choline (24%). 3. Electrically-evoked [3H]-ACh release was abolished by tetrodotoxin (TTX: 300 nM) and unaffected by hexamethonium (10 microM), indicating a postganglionic event. It was reduced by physostigmine (100 nM) and the muscarinic receptor agonist, muscarone (10 nM-1 microM), and enhanced by atropine (0.1-100 nM). These findings indicate the presence of a muscarinic negative feedback mechanism controlling ACh release. 4. The effects of various subtype-preferring muscarinic receptor antagonists were evaluated on [3H]-ACh release and muscle contraction. The rank potency (-log EC50) orders at pre- and postjunctional level were: atropine > or = 4-diphenyl-acetoxy-N-piperidine (4-DAMP) > mamba toxin 3 (MT-3) > tripitramine > para-fluorohexahydrosiladiphenidol (pF-HHSiD) > or = methoctramine > or = pirenzepine > tripinamide, and atropine > or = 4-DAMP > pF-HHSiD >> pirenzepine = tripitramine > tripinamide > methoctramine >> MT-3, respectively. 5. The comparison of pre- and post-junctional potencies and the relationship analysis with the affinity constants at human cloned muscarinic receptor subtypes indicates that the muscarinic autoreceptor inhibiting ACh release in human detrusor is an M4 receptor, while the receptor involved in muscular contraction belongs to the M3 subtype.