Characterization of the endokinins: human tachykinins with cardiovascular activity

Abstract

We report four human tachykinins, endokinins A, B, C, and D (EKA-D), encoded from a single tachykinin precursor 4 gene that generates four mRNAs (alpha, beta, gamma, and delta). Tachykinin 4 gene expression was detected primarily in adrenal gland and in the placenta, where, like neurokinin B, significant amounts of EKB-like immunoreactivity were detected. EKA/B 10-mers displayed equivalent affinity for the three tachykinin receptors as substance P (SP), whereas a 32-mer N-terminal extended form of EKB was significantly more potent than EKA/B or SP. EKC/D, which possess a previously uncharacterized tachykinin motif, FQGLL-NH(2), displayed low potency. EKA/B displayed identical hemodynamic effects to SP in rats, causing short-lived falls in mean arterial blood pressure associated with tachycardia, mesenteric vasoconstriction, and marked hindquarter vasodilatation. Thus, EKA/B could be the endocrineparacrine agonists at peripheral SP receptors and there may be as yet an unidentified receptor(s) for EKC/D.

Figure 1

(A) Amino acid sequence alignment and homologies of human α, β, γ, and δTAC4 and mouse TAC4. (B) Intron/exon organization of the human TAC4 gene transcripts.

Figure 2

Alignment of the amino acid sequences of the mammalian tachykinins.

Figure 3

(A) Semiquantitative PCR analysis of the tissue distribution of the human α, β, γ, δTAC4, and TAC1 transcripts in 24 human tissues. Expression is normalized to that of the human β-actin transcript. (B) Semiquantitative PCR analysis of the distribution of the human α, β, γ, δTAC4, and TAC1 transcripts, and that of the NK₁ receptor, in 15 human peripheral cell lines. Expression is normalized to that of the hGAPDH transcript. (C) Semiquantitative PCR analysis of the tissue distribution of the mouse TAC4 and TAC1 transcripts in 20 mouse tissues. Expression is normalized to that of the mGAPDH transcript.

Figure 4

Binding of tachykinin ligands to the human NK₁ (A), NK₂ (B), and NK₃ (C) receptors. The binding of tachykinin ligands (■, SP; ⧫, mHK-1; ▴, NKA; ●, [N-Me-Phe⁷]NKB; □, EKA/B; ○, EKC; ◊, EKD; ▵, SB 222200) as determined and described in Materials and Methods by using [³H] SR140333 at the human NK₁ receptor, [³H] SR48968 at the human NK₂ receptor, and [³H] SR142801 at the human NK₃ receptor. The data are from representative experiments previously replicated in Table 1.

Figure 5

Regional hemodynamic effects of SP and EKA/B (A, ● and ○) and EKC and EKD (B, ● and ○) in conscious male rats (six in each group). There were no significant differences between the integrated effects of equimolar doses of SP and EKA/B with no measurable hemodynamic effects in the vehicle-treated controls.