Selective inhibition by dactinomycin of NANC sensory bronchoconstriction and [125I]NKA binding due to NK-2 receptor antagonism.
In the present study, dactinomycin (10(-5) M) inhibited the non-adrenergic, non-cholinergic bronchoconstriction upon antidromic vagal nerve stimulation (1 Hz for 1 min) in the isolated perfused guinea-pig lung by 84%. The release of calcitonin gene-related peptide was unchanged, however, suggesting a postjunctional action. Dactinomycin (10(-5), 5 x 10(-5) M) also reduced non-adrenergic non-cholinergic bronchial contractions (maximally by 75%) induced by electrical field stimulation or capsaicin, while the cholinergic component and non-adrenergic non-cholinergic relaxation remained intact. The neurokinin-2 receptor antagonist L-659,877 (10(-6) M) had a similar effect as dactinomycin, inhibiting the non-adrenergic non-cholinergic bronchial contractions by 69%, while the neurokinin-1 receptor antagonist CP-96,345 (10(-6) M) had no effect. The bronchoconstriction evoked by neurokinin A, the selective neurokinin-2 receptor agonist Nle10neurokinin A (4-10) and capsaicin was markedly inhibited by dactinomycin while the contraction induced by substance P (SP), the selective neurokinin-1 receptor agonist Sar9Met(O2)11SP, endothelin-1 and acetylcholine was not affected. In autoradiographic experiments on guinea-pig lung, [125I]neurokinin A-labelled sections showed dense binding in the bronchial smooth muscle layer. Dactinomycin inhibited the specific binding of [125I]neurokinin A in a concentration-dependent manner (IC50 = 6.3 x 10(-6) M) and 66% of [125I]neurokinin A total binding was inhibited by 10(-4) M dactinomycin. In the rat colon, [125I]neurokinin A binding to neurokinin-2 sites on circular smooth muscle was inhibited by dactinomycin with an IC50 value of 7.9 x 10(-6) M. Dactinomycin failed to reduce increased nerve-evoked contractions or those caused by Nle10neurokinin A (4-10) per se in the rat vas deferens, which are considered to be mediated by neurokinin-2 receptor activation. In the rat portal vein, dactinomycin did not influence the contractions caused by the neurokinin-3 selective agonist Pro7neurokinin B. In conclusion, dactinomycin selectively inhibited neurokinin-2 receptor activation in guinea-pig lung and rat colon, but not in rat vas deferens, which may depend on the existence of different neurokinin-2 receptor subtypes. Neurokinin A is most likely the main endogenous excitatory non-adrenergic non-cholinergic transmitter in guinea-pig bronchi.
Lou
Y P
YP
Department of Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Delay-Goyet
P
P
Lundberg
J M
JM
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism; D016084:Bronchoconstriction / Q000187:drug effects* / Q000502:physiology; D003609:Dactinomycin / Q000494:pharmacology*; D004558:Electric Stimulation; D016232:Endothelins / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D015288:Neurokinin A / Q000378:metabolism* / Q000494:pharmacology; D018041:Receptors, Neurokinin-2; D017981:Receptors, Neurotransmitter / Q000037:antagonists & inhibitors; D014630:Vagus Nerve / Q000502:physiology
D016232:Endothelins; D018041:Receptors, Neurokinin-2; D017981:Receptors, Neurotransmitter; D003609:Dactinomycin; D015288:Neurokinin A; D000109:Acetylcholine