Identification of both NK1 and NK2 receptors in guinea-pig airways.
1. NK1 and NK2 receptors have been characterized in guinea-pig lung membrane preparations by use of [125I-Tyr8]-substance P and [125I]-neurokinin A binding assays in conjunction with tachykinin-receptor selective agonists ([Sar9Met(O2)11]substance P for NK1 and [beta Ala8]neurokinin A (4-10) for NK2) and antagonists (CP-99,994 for NK1 and SR48968 for NK2). 2. The presence of high affinity, G-protein-coupled NK1 receptors in guinea-pig lung parenchymal membranes has been confirmed. The rank order of affinity for competing tachykinins was as predicted for an NK1 receptor: substance P = [Sar9Met(O2)11]substance P > substance P-methyl ester = physalaemin > neurokinin A = neurokinin B >> [beta Ala8]neurokinin A (4-10). The novel NK1 antagonist CP-99,994 has a Ki of 0.4 nM at this NK1 site. 3. In order to characterize [125I]-neurokinin A binding to guinea-pig lung, the number of [125I]-neurokinin A specific binding sites was increased 3-4 fold by purification of the parenchymal membranes over discontinuous sucrose gradients. The rank order of affinity determined for NK1- and NK2-receptor agonists and antagonists in competition for these sites showed that the majority (80%) of [125I]-neurokinin A specific binding was also to the NK1 receptor. 4. Under conditions where the guinea-pig lung parenchymal NK1 receptor was fully occupied by a saturating concentration of either [Sar9Met(O2)11]substance P (1 microM) or CP-99,994 (2.7 microM), residual [125I]-neurokinin A specific binding was inhibited in a concentration-dependent manner by both [beta Ala8]neurokinin A and SR48968. This result shows that the NK2 receptor is also present in these preparations. 5. Similar studies using guinea-pig tracheal membranes demonstrated that [125I]-neurokinin A specific binding was composed of a NK1-receptor component (60%), inhibited by both [Sar9Met(02)11]substance P and CP-99,994, and a significant NK2-receptor component, inhibited by both [beta Ala 8]neurokinin A andSR48968.6. In summary, these data demonstrate that guinea-pig lung parenchyma and guinea-pig trachea express both NK1 and NK2 receptors.
McKee
K T
KT
Department of Pharmacology, Merck Frosst Centre for Therapeutic Research, Pointe-Claire, Dorval, Québec, Canada.
Millar
L
L
Rodger
I W
IW
Metters
K M
KM
D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008168:Lung / Q000187:drug effects / Q000378:metabolism; D008297:Male; D015288:Neurokinin A / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000494:pharmacology; D064729:Neurokinin-1 Receptor Antagonists; D010446:Peptide Fragments / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011869:Radioligand Assay; D018040:Receptors, Neurokinin-1 / Q000187:drug effects / Q000378:metabolism*; D018041:Receptors, Neurokinin-2 / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D012137:Respiratory System / Q000187:drug effects / Q000378:metabolism*; D013373:Substance P / Q000031:analogs & derivatives / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects / Q000378:metabolism
D001549:Benzamides; D007457:Iodine Radioisotopes; D064729:Neurokinin-1 Receptor Antagonists; D010446:Peptide Fragments; D010880:Piperidines; D018040:Receptors, Neurokinin-1; D018041:Receptors, Neurokinin-2; C062618:substance P, Sar(9)-Met(O2)(11)-; C064218:neurokinin A (4-10), beta-Ala(8)-; C080755:3-(2-methoxybenzylamino)-2-phenylpiperidine; D013373:Substance P; C073839:SR 48968; D015288:Neurokinin A