title: Some characterization of the responses to substance P and other tachykinins in rabbit iris sphincter muscle.
abstract: Contractile responses to substance P, physalaemin and eledoisin, three members of the tachykinin family, were compared and characterized in rabbit iris sphincter smooth muscle. Eledoisin and physalaemin were approximately 5 times more potent than substance P, and the maximum responses to substance P and physalaemin were about 85 percent of those to eledoisin and carbachol. The contractile responses to the three tachykinins were not affected by tetrodotoxin (3 X 10(-6) M) and atropine (10(-6) M). The contractions induced by substance P and physalaemin were well sustained even after they were thoroughly washed out, whereas the eledoisin-induced contraction was rapidly ceased by removing the agonist from the bathing medium. The sustained contraction evoked by substance P or physalaemin was strongly dependent on extracellular calcium ions. Phenoxybenzamine (2 X 10(-5) M, 10 min) selectively attenuated the response to eledoisin, but not substance P or physalaemin, and concomitant incubation with excess eledoisin (10(-7) M) significantly prevented the inhibitory effect of phenoxybenzamine. The difference between responses to eledoisin and to the other peptides, substance P and physalaemin, may suggest the existence of two different receptor subtypes for tachykinins in rabbit iris sphincter smooth muscle.
authors.forename: R
authors.initials: R
authors.lastname: Hosoki
authors.forename: T
authors.initials: T
authors.lastname: Hisayama
authors.forename: I
authors.initials: I
authors.lastname: Takayanagi
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D004600:Eledoisin / Q000494:pharmacology*; D066298:In Vitro Techniques; D007498:Iris / Q000187:drug effects*; D007705:Kinins / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D010643:Phenoxybenzamine / Q000494:pharmacology; D010803:Physalaemin / Q000494:pharmacology*; D011817:Rabbits; D013373:Substance P / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D007705:Kinins; D010643:Phenoxybenzamine; D010803:Physalaemin; D013373:Substance P; D013779:Tetrodotoxin; D004600:Eledoisin; D001285:Atropine; D002217:Carbachol