Functional antagonism between nitric oxide and ATP in the motor responses of guinea-pig ileum.
1. The interaction of nitric oxide and ATP in the non-adrenergic, non-cholinergic (NANC) motor responses and the presence of NADPH-diaphorase and quinacrine-positive myenteric neurones were studied on guinea-pig ileum using mechanographic, histochemical and quinacrine-fluorescence techniques. In the presence of phentolamine, propranolol and atropine, the non-precontracted longitudinally oriented organ bath preparations responded to sodium nitroprusside (1-100 microM) or ATP (5-50 microM) with tetrodotoxin (0.1 microM)-resistant relaxation or contraction, respectively. The effects of ATP were suramin (50 microM)- and apamin (5 microM)-sensitive. 2. The NANC motor responses elicited by electrical stimulation (0.8 ms, 1-20 Hz, 20 s) consisted of tetrodotoxin-sensitive relaxation phase followed by a phase of twitch-like and tonic contractions. 3. NG-nitro-L-arginine (L-NNA, 0.1-0.5 mM) inhibited or abolished the relaxation phase. L-arginine (0.5 mM), but not D-arginine (0.5 mM), restored the relaxation phase in L-NNA-pretreated preparations. The relaxation phase increased after ATP-induced desensitization of purinoceptors and in the presence of suramin (50 mciroM) but was abolished by apamin (5 microM). 4. The phase of contractions was enhanced by L-NNA (0.1-0.5 mM) and restored by L-arginine (0.5 mM). The twitch-like and tonic contractions were decreased during ATP-induced purinoceptor desensitization and in the presence of suramin (50 microLM). Apamin (5 microM) inhibited the tonic contractions. 5. The desensitization of purinoceptors by ATP did not change the L-NNA-induced inhibition of the relaxation phase but decreased the L-NNA-increased phase of contractions. L-NNA reduced the relaxation phase and increased the phase of contractions during purinoceptor desensitization. 6. We conclude that in the longitudinal muscle layer of the guinea-pig ileum, nitric oxide mediates the relaxation phase while ATP contributes via smooth muscle P2 purinoceptors to the phase of contractions suggesting a postjunctional functional antagonism between nitric oxide and ATP. The presence of NADPH-diaphorase- and quinacrine-positive neuronal cells and processes running to the muscle cells confirms a physiological role of nitric oxide and ATP in the ileal neurotransmission.
Ivancheva
C
C
Institute of Physiology, Bulgarian Academy of Sciences, Sofia.
Itzev
D
D
Radomirov
R
R
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009252:NADPH Dehydrogenase / Q000378:metabolism; D009569:Nitric Oxide / Q000502:physiology*; D019335:Nitroarginine / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D018048:Receptors, Purinergic P2 / Q000502:physiology; D009435:Synaptic Transmission
D018048:Receptors, Purinergic P2; D009599:Nitroprusside; D019335:Nitroarginine; D001030:Apamin; D009569:Nitric Oxide; D000255:Adenosine Triphosphate; D009252:NADPH Dehydrogenase