Purification, structural characterization, and myotropic activity of a peptide related to des-Arg⁹-bradykinin from an elasmobranch fish, the little skate, Leucoraja erinacea

A bradykinin (BK)-related peptide was isolated from heat-denaturated plasma from an elasmobranch fish, the little skate, Leucoraja erinacea after incubation with porcine pancreatic kallikrein. The primary structure of the peptide (H-Gly-Ile-Thr-Ser-Trp-Leu-Pro-Phe-OH; skate BK) shows limited structural similarity to the mammalian B1 receptor agonist, des-Arg⁹-BK. The myotropic activities of synthetic skate BK, and the analog skate [Arg⁹]BK, were examined in isolated skate vascular and intestinal smooth muscle preparations. Skate BK produced a concentration-dependent constriction of the mesenteric artery (EC₅₀ = 4.37 × 10^-8 M; maximum response = 103.4 ± 10.23% of the response to 60 mM KCl) but the response to skate [Arg⁹]BK was appreciably weaker (response to 10^-6 M = 73.0 ± 23.4% of the response to 60 mM KCl). Neither the first branchial gill arch nor the ventral aorta responded to either purified peptide. Skate BK also produced a concentration-dependent constriction of intestinal smooth muscle preparations (EC₅₀ = 2.74 × 10^-7 M; maximum response 31.0 ± 12.2% of the response to 10^-5 M acetylcholine). Skate [Arg⁹]BK was without effect on the intestinal preparation. The data provide evidence for the existence of the kallikrein-kinin system in a phylogenetically ancient vertebrate group and the greater potency of skate BK compared with the analog skate [Arg⁹]BK suggests that the receptor mediating vascular responses resembles the mammalian B1 receptor more closely than the B2 receptor.