Otenzepad shows two populations of binding sites in human gastric smooth muscle

Cholinergic agonists and antagonists frequently used for gastrointestinal motility disorders often produce adverse effects. A possible explanation for this is the presence of similar muscarinic receptor subtypes on smooth muscle from different gastrointestinal organs. The aim of this study was to characterize muscarinic receptor subtypes in human gastric smooth muscle with receptor binding methods. N-[3H]Methylscopolamine ([3H]NMS) saturation experiments showed a homogeneous population of noninteracting binding sites (KD = 0.76 ± 0.07 nM, Bmax = 46.94 ± 3.69 fmol/mg of tissue protein, nH = 0.99 ± 0.01). The rank order of inhibition of [3H]NMS binding by nonlabelled compounds was atropine [Formula: see text] otenzepad [Formula: see text] pirenzepine. Atropine and pirenzepine bound to a homogeneous population of binding sites. The inhibition of [3H]NMS binding by otenzepad showed two populations of receptors (nH < 1, p < 0.01), whose apparent Ki1 of 298 ± 40 nM and apparent Ki2 of 3.463 ± 0.62 mM were similar to those reported for the M2 and M3 muscarinic receptor subtypes. The M2 subtype was the more abundant of the two, representing 79.12 ± 5.48% of the total population. We conclude that two muscarinic receptor subpopulations similar to the M2 and M3 subtypes are present in human gastric smooth muscle and that the M2-like receptor is the more abundant of the two.Key words: human stomach, muscarinic receptor subtypes, smooth muscle.

Actions of cholinergic agonists and antagonists on sensory nerve endings in rat skin, in vitro

1. Cholinergic effects on primary sensory afferents were investigated in a superfused skin-saphenous nerve preparation of the rat that allows the application of chemicals topically to the corium side of identified receptive fields. 2. The acetylcholine analogue carbachol (carbamoylcholine) selectively excited cutaneous C-fibers of nociceptive character; in proportion, almost half of the mechanoheat sensitive ("polymodal," C-MH, n = 27), and a third of the mechanocold sensitive (C-MC, n = 10), and high-threshold mechanosensitive (C-HTM, n = 6) C-fibers were activated. 3. None of slowly and rapidly adapting A beta fibers, low and high threshold mechanoreceptive A delta fibers (n = 19) gave a response to high concentrations (< or = 10(-4) M) of carbachol. 4. The carbachol threshold concentrations of C-nociceptors ranged between 10(-7) and 10(-4) M; 10(-6) M was most frequently encountered. 5. The carbachol-induced discharges showed a dose-response relationship without obvious "ceiling" from 10(-6) to 10(-4) M. Tachyphylaxis was not prominent; the fibers mostly developed ongoing activity after exposure to carbachol. 6. Repeated carbachol treatment of C-MH units left with a marked and sustained desensitization to mechanical (von Frey) stimulation, while the heat responsiveness remained unchanged. 7. In a group of carbachol-sensitive C-nociceptors (n = 4), two units could also be excited with muscarine (10(-6) M), one with nicotine (10(-6) M), and one unit with both substances.(ABSTRACT TRUNCATED AT 250 WORDS)