Involvement of nitric oxide in the non‐adrenergic non‐cholinergic neurotransmission of horse deep penile arteries: role of charybdotoxin‐sensitive K+‐channels

• Published in: British journal of pharmacology Vol. 116; no. 6; pp. 2582 - 2590
• Main Authors: Simonsen, Ulf, Prieto, Dolores, Tejada, Ifñgo Sáenz, Garcia‐Sacristan, Albino
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.11.1995; Nature Publishing
• Subjects: 8‐Br‐cyclic GMP; Adrenergic Fibers - drug effects; Adrenergic Fibers - enzymology; Adrenergic Fibers - physiology; Animals; Arginine - analogs & derivatives; Arginine - pharmacology; Arginine - physiology; Biological and medical sciences; Blood vessels and receptors; Ca2+‐activated K+‐channels; charybdotoxin; Charybdotoxin - pharmacology; Cholinergic Fibers - drug effects; Cholinergic Fibers - enzymology; Cholinergic Fibers - physiology; Electric Stimulation; electrical field stimulation; Endothelium, Vascular - drug effects; Endothelium, Vascular - enzymology; Endothelium, Vascular - innervation; Fundamental and applied biological sciences. Psychology; Glyburide - pharmacology; Horses; Male; Methylene Blue - pharmacology; Muscle Relaxation - drug effects; Muscle Relaxation - physiology; Muscle, Smooth, Vascular - drug effects; Muscle, Smooth, Vascular - enzymology; Muscle, Smooth, Vascular - innervation; NADPH Dehydrogenase - metabolism; Nerve Fibers - drug effects; Nerve Fibers - enzymology; Nerve Fibers - physiology; NG‐nitro‐L‐arginine; nitrergic nerves; nitric oxide; Nitric Oxide - physiology; Nitroarginine; Oxyhemoglobins - pharmacology; Penile arteries; Penis - blood supply; Penis - drug effects; Potassium Channels - drug effects; Potassium Channels - physiology; Sensitivity and Specificity; Signal Transduction - drug effects; Signal Transduction - physiology; Synaptic Transmission - drug effects; Synaptic Transmission - physiology; Vertebrates: cardiovascular system; Non adrenergic non cholinergic transmission; Smooth muscle; Male genital system; In vitro; Artery; Signal transduction; Vertebrata; Mammalia; Penis; Horse; Nitrogen monoxide; Neurotransmitter; Circulatory system; Perissodactyla; Endothelium derived relaxing factor; Ungulata
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1995.tb17211.x

1 . The involvement of nitric oxide (NO) and the signal transduction mechanisms mediating neurogenic relaxations were investigated in deep intracavernous penile arteries with an internal lumen diameter of 600–900 μm, isolated from the corpus cavernosum of young horses. 2 . The presence of nitric oxide synthase (NOS)‐positive nerves was examined in cross and longitudinal sections of isolated penile arteries processed for NADPH‐diaphorase (NADPH‐d) histochemistry. NADPH‐d‐positive nerve fibres were observed in the adventitia‐media junction of deep penile arteries and in relation to the trabecular smooth muscle. 3 . Electrical field stimulation (EFS) evoked frequency‐dependent relaxations of both endothelium‐intact and denuded arterial preparations treated with guanethidine (10−5 m) and atropine (10−7 m), and contracted with 10−6 m phenylephrine. These EFS‐induced relaxations were tetrodotoxin‐sensitive indicating their non‐adrenergic non‐cholinergic (NANC) neurogenic origin. 4 . EFS‐evoked relaxations were abolished at the lowest frequency (0.5‐2 Hz) and attenuated at higher frequencies (4–32 Hz) by the NOS inhibitor, NG‐nitro‐L‐arginine (L‐NOARG, 3 × 10−5m). This inhibitory effect was antagonized by the NO precursor, L‐arginine (3 × 10−3 m). NG‐nitro‐D‐arginine (10−4 m) did not affect the relaxations to EFS. 5 . Incubation with either the NO scavenger, oxyhaemoglobin (10−5 m), or methylene blue (10−5 m), an inhibitor of guanylate cyclase activation by NO, caused significant inhibitions of the EFS‐evoked relaxations, and while oxyhaemoglobin abolished the relaxations to exogenously added NO (acidified sodium nitrite, 10−6‐10−3m), there still persisted a relaxation to NO of 24.4 ± 5.1% (n = 6) in the presence of methylene blue. 6 . Glibenclamide (3 × 10−6 m), an inhibitor of ATP‐activated K+‐channels, did not alter the relaxations to either EFS‐stimulation or NO, while the blocker of Ca2+‐activated K+‐channels, charybdotoxin (3 × 10−8 m), caused a significant inhibition of both the electrically‐induced relaxations and the relaxations to exogenously added NO. Furthermore, charybdotoxin blocked relaxations induced by the cell permeable analogue of cyclic GMP, 8‐bromo cyclic GMP (8 Br‐cyclic GMP). 7 . These results suggest that relaxations of horse deep penile arteries induced by NANC nerve stimulation involve mainly NO or a NO‐like substance from nitrergic nerves. NO would stimulate the accumulation of cyclic GMP followed by increases in the open probability of Ca2+‐activated K+‐channels and hyperpolarization leading to relaxation of horse penile arteries.