ABSTRACT
PURPOSE: Stimulating muscarinic receptors in pig bladder urothelium causes the release of a diffusable factor that inhibits contractions of the underlying detrusor muscle. We investigated whether the contractions of human detrusor strips elicited by the muscarinic agonist carbachol, electrical field stimulation, KCl or the neurokinin receptor agonist neurokinin A are affected by the urothelium. MATERIALS AND METHODS: Paired intact and urothelium denuded muscle strips were placed in modified gassed Tyrode's solution at 37C. Cumulative concentration-response curves to carbachol or KCl were constructed. In other tissues the strips were stimulated electrically (1 to 40 Hz) with trains of square wave pulses 20 seconds in duration at 5-minute intervals. RESULTS: Cholinergic contractions evoked by electrical field stimulation at 10 and 30 Hz or by carbachol were significantly inhibited in the presence of an intact urothelium. Contractions elicited by KCl and by 10 microM neurokinin A were not modified by the urothelium. The urothelium mediated inhibition of contractions induced by carbachol was not affected by 300 microM L-NG-nitroarginine, 1 microM ODQ (1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one), 1 microM propranolol or 5 microM indomethacin. CONCLUSIONS: Muscarinic agonists stimulate the release of an inhibitory factor from the human urothelium. The factor is distinct from nitric oxide and it persists in the presence beta-adrenoceptor blockade or cyclooxygenase inhibition.
Subject(s)
Carbachol/pharmacology , Muscarinic Agonists/pharmacology , Muscle Contraction/physiology , Muscle Hypertonia/physiopathology , Muscle, Smooth/physiopathology , Tissue Extracts/physiology , Urothelium/physiopathology , Aged , Culture Techniques , Dose-Response Relationship, Drug , Electric Stimulation , Female , Humans , Male , Middle Aged , Muscle Contraction/drug effects , Muscle, Smooth/drug effects , Neurokinin A/pharmacology , Potassium Chloride/pharmacology , Stimulation, Chemical , Urothelium/drug effectsABSTRACT
The effects of K(ATP) channel blockers (glibenclamide, HMR 1883, HMR 1372) and openers (cromakalim, pinacidil, diazoxide) on the electrically-evoked (5 Hz) release of [(3)H]acetylcholine were studied in isolated guinea-pig atria and myenteric plexus-longitudinal muscle preparations which had been preincubated with [(3)H]choline. Atria: Cromakalim (0.3 microM and 1 microM), pinacidil (10 microM) and diazoxide (30 microM) significantly reduced the stimulation-evoked release of [(3)H]acetylcholine. The inhibition produced by cromakalim and pinacidil was prevented by 1 microM of either HMR 1883, HMR 1372 or glibenclamide. The blockers alone significantly increased the release at concentrations of 30 microM, whereas 1 microM and 10 microM had no effect. Myenteric plexus-longitudinal muscle preparation: The electrically-evoked release of [(3)H]acetylcholine was not affected by K(ATP) channel blockers or openers. In contrast, the contractions of the longitudinal muscle caused by electrical stimulation or by carbachol were strongly inhibited by 1 microM cromakalim which suggests that the relaxant effect of the K(ATP) channel openers is exclusively a direct effect on intestinal smooth muscle. The findings suggest that blockade of activated K(ATP) channels in vagal nerves of guinea-pig atria stimulates acetylcholine release, and that this effect may contribute to the antiarrhythmic actions of K(ATP) channel blockers. By contrast, release of acetylcholine from guinea-pig myenteric plexus is not modulated by K(ATP) channels which suggests heterogeneity of K(ATP) channel distribution in peripheral autonomic nerves.
Subject(s)
Acetylcholine/metabolism , Intestine, Small/drug effects , Neuromuscular Junction/drug effects , Potassium Channels/physiology , Thiourea/analogs & derivatives , Animals , Atrial Function , Cromakalim/pharmacology , Diazoxide/pharmacology , Female , Glyburide/pharmacology , Guinea Pigs , Heart Atria/drug effects , Heart Atria/metabolism , In Vitro Techniques , Intestine, Small/metabolism , Intestine, Small/physiology , Male , Muscle, Smooth/drug effects , Muscle, Smooth/metabolism , Muscle, Smooth/physiology , Myenteric Plexus/drug effects , Myenteric Plexus/metabolism , Myenteric Plexus/physiology , Myocardial Contraction/drug effects , Neuromuscular Junction/metabolism , Neuromuscular Junction/physiology , Pinacidil/pharmacology , Potassium Channel Blockers/pharmacology , Potassium Channels/agonists , Sulfonamides/pharmacology , Thiourea/pharmacologyABSTRACT
1. The effects of anandamide on [3H]-acetylcholine release and muscle contraction were studied on the myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum preincubated with [3H]-choline. 2. Anandamide increased both basal [3H]-acetylcholine release (pEC(50) 6.3) and muscle tone (pEC(50) 6.3). The concentration-response curves for anandamide were shifted to the right by 1 microM capsazepine (pK(B) 7.5 and 7.6), and by the combined blockade of NK1 and NK3 tachykinin receptors with the antagonists CP99994 plus SR142801 (each 0.1 microM). The CB1 and CB2 receptor antagonists, SR141716A (1 microM) and SR144528 (30 nM), did not modify the facilitatory effects of anandamide. 3. Anandamide inhibited the electrically-evoked release of [3H]-acetylcholine (pEC(50) 5.8) and contractions (pEC(50) 5.2). The contractile response to the muscarinic agonist methacholine was not significantly affected by 10 microM anandamide. 4. The inhibitory effects of anandamide were not changed by either capsazepine (1 microM), SR144528 (30 nM) or CP99994 plus SR142801 (each 0.1 microM). SR141716A (1 microM) produced rightward shifts in the inhibitory concentration-response curves for anandamide yielding pK(B) values of 6.6 and 6.2. 5. CP55940 inhibited the evoked [3H]-acetylcholine release and contractions, and SR141716A (0.1 microM) shifted the concentration-response curves of CP55940 to the right with pK(B) values of 8.4 and 8.9. 6. The experiments confirm the existence of release-inhibitory CB1 receptors on cholinergic myenteric neurones. We conclude that anandamide inhibits the evoked acetylcholine release via stimulation of a receptor that is different from the CB1 and CB2 receptor. Furthermore, anandamide increases basal acetylcholine release via stimulation of vanilloid receptors located at primary afferent fibres.
Subject(s)
Acetylcholine/metabolism , Arachidonic Acids/pharmacology , Capsaicin/analogs & derivatives , Ileum/drug effects , Receptors, Drug/physiology , Animals , Camphanes/pharmacology , Capsaicin/pharmacology , Cyclohexanols/pharmacology , Dose-Response Relationship, Drug , Electric Stimulation , Endocannabinoids , Guinea Pigs , Ileum/metabolism , In Vitro Techniques , Male , Methacholine Chloride/pharmacology , Muscle Contraction/drug effects , Piperidines/pharmacology , Polyunsaturated Alkamides , Pyrazoles/pharmacology , Receptors, Cannabinoid , RimonabantABSTRACT
The effects of the nitric oxide (NO) donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) and the NO synthase inhibitor L-N(G)-nitroarginine (L-NOARG) on the electrically evoked [(3)H]-acetylcholine release were studied in an epithelium-free preparation of guinea-pig trachea that had been preincubated with [(3)H]-choline. SNAP (100 and 300 microM) caused small but significant increases of the electrically evoked [(3)H]-acetylcholine release (121+/-4% and 124+/-10% of control). Resting outflow of [(3)H]-ACh was not affected by SNAP. The increase by SNAP was abolished by the specific inhibitor of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ, 1 microM). The facilitatory effect of SNAP (100 and 300 microM) was reversed into inhibition of release (to 74+/-4% and to 78+/-2%) after pretreatment of the trachea with capsaicin (3 microM). ODQ prevented the inhibition. Capsaicin pretreatment alone did not significantly alter the release of [(3)H]-acetylcholine. A significant inhibition by SNAP (100 microM) of [(3)H]-acetylcholine release (78+/-3%) was also seen in the presence of the NK(2) receptor antagonist SR 48968 (30 nM). L-NOARG (10 and 100 microM) significantly enhanced the electrically-evoked smooth muscle contractions, but caused no significant increases of the evoked release from capsaicin pretreated trachea strips. This might indicate that the inhibitory effect of endogenous NO on acetylcholine release is too small to be detected by overflow studies. It is concluded that NO has dual effects on the evoked acetylcholine release. NO enhances release in the absence of modifying drugs, but NO inhibits acetylcholine release after blockade of the NK(2) receptor or after sensory nerve depletion with capsaicin. This suggests that NO and endogenous tachykinins act in series to produce an increase in acetylcholine release.