Physalaemin

Physalaemin: an amphibian tachykinin in human lung small-cell carcinoma

Immunoreactivity to the amphibian peptide physalaemin was characterized from extracts of a human lung small-cell carcinoma by immunological, chemical, and pharmacological means. Tumor-related peptide cross-reacted with three antiserums to physalaemin to yield 1.1 to 1.6 nanomoles per gram of tissue. Physalaemin and tumor peptide had similar retention times on high-performance liquid chromatography after chemical and enzymic modifications that included pH changes, oxone oxidation, use of a hydrophilic ion-pairing reagent, and digestion with trypsin and pyroglutamate aminopeptidase. Both physalaemin and the tumor peptide produced a contractile response of isolated guinea pig ileum at threshold concentrations of approximately 100 to 150 picograms per milliliter. These data suggest that small-cell carcinoma of the lung contains a physalaemin-like peptide that has structural and biological homology to its amphibian counterpart.

Contractile responses induced by physalaemin, an analogue of substance P, in the rat esophagus

We examined the effects of physalaemin, an agonist of tachykinin receptors, on mechanical responses in the rat esophagus to clarify possible regulatory roles of tachykinins in esophageal motility. Exogenous application of physalaemin caused tonic contractions in rat esophageal segments when tension was recorded in the longitudinal direction but not when tension was recorded in the circular direction. The physalaemin-evoked contractions were blocked by pretreatment with nifedipine, a blocker of L-type calcium channels in both striated and smooth muscle cells. However, tetrodotoxin, a blocker of voltage-dependent sodium channels in striated muscle cells and neurons, did not affect the physalaemin-induced contractions. These results indicate that physalaemin might induce contractile responses in longitudinal smooth muscle of the muscularis mucosa via direct actions on muscle cells but not on neurons. Although pretreatment with a tachykinin NK(1) receptor antagonist, N-acetyl-l-tryptophan 3,5-bis (trifluoromethyl) benzyl ester (L-732,138), did not significantly affect the physalaemin-evoked contractions in rat esophageal segments, a tachykinin NK(2) receptor antagonist, (S)-N-methyl-N[4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl) butyl] benzamide (SR48968), and a tachykinin NK(3) receptor antagonist, (S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl) piperidin-3-yl)propyl)-4-phenylpiperidin-4-yl)-N-methylacetamide (SR142801), significantly inhibited the physalaemin-evoked contractions. These results suggest that tachykinins can activate longitudinal contraction of smooth muscle in the muscularis mucosa, mediated via tachykinin NK(2) and NK(3) receptors on muscle cells, in the rat esophagus.

Conformation of physalaemin

The conformational and spatial configuration of the biologically active undecapeptide physalaemin was studied using 350-MHz1H NMR. The NMR analyses suggested the existence of a strong hydrogen bond between the amide proton of the Phe7 and a carbonyl group in the N-terminal moiety, most likely the Pro4 one. Other bondings were postulated, involving the side-chain amine of Lys6 and the side-chain amide of Asn5 and respectively the side-chain carboxyl of Asp3 and the terminal amide carbonyl of Met-NH2. Thus unlike its shorter peptidic fragments, physalaemin exhibited a stable molecular structure in solution, giving some insight into the conformation required for interaction at the biological receptor of tachykinins.

Parallel bioassay of physalaemin and hylambatin on smooth muscle preparations and blood pressure

J Pharm Pharmacol.1984 Apr;36(4):284-6.PMID:6144787DOI: 10.1111/j.2042-7158.1984.tb04374.x.

Hylambatin, a novel tachykinin endecapeptide isolated from the skin of the African frog Hylambates maculatus, must be ascribed to the physalaemin subfamily. It differs structurally from all other known tachykinins mainly in having a methionine residue replacing the usual leucine residue at position 2 from the C-terminus. In parallel bioassay on a number of in-vitro and in-vivo test objects, hylambatin and physalaemin were nearly indistinguishable from each other, with few moderate quantitative differences.

Chemoreceptor responses to substance P, physalaemin and eledoisin: evidence for neurokinin-1 receptors in the cat carotid body

Neurosci Lett.1990 Dec 11;120(2):183-6.PMID:1705679DOI: 10.1016/0304-3940(90)90033-6.

Substance P (SP) belongs to a group of peptides called tachykinins. Biological effects of SP are mediated by tachykinin receptors that have been classified as neurokinin-1 (NK-1), NK-2 and NK-3 subtypes. The aim of the present study is to elucidate the tachykinin receptor subtype(s) that mediate the excitatory effects of SP in the carotid body. For this purpose, we compared the carotid body responses elicited by SP with that of physalaemin and eledoisin. In other tissues, physalaemin exhibits equi or greater potency at NK-1 receptors and eledoisin exerts its effects more on NK-2 and NK-3 subtypes compared to SP. Experiments were performed on eight cats that were anaesthetized, paralyzed and artificially ventilated with room air. Close carotid body administration of SP and physalaemin produced dose-dependent augmentation of the chemoreceptor afferent activity. Chemoreceptor discharge, however, was unaffected by eledoisin. Compared to that by SP, the magnitude of excitation produced by physalaemin was the same at lower doses but significantly greater with the highest dose (100 nmol). The time course of the response induced by physalaemin, however, was the same as that by SP. The present results demonstrate that in the carotid body physalaemin is also either equi or relatively more potent than SP, whereas eledoisin has no effect on the chemoreceptor discharge. It is suggested that stimulation of the carotid body by SP is mediated by NK-1 but not NK-2 or NK-3 receptors.