CHARACTERIZATION OF KININ RECEPTORS MODULATING NEUROGENIC CONTRACTIONS OF THE MOUSE ISOLATED VAS-DEFERENS

1 This study analyses the receptors mediating the effects of bradykini n (BK) and analogues on neurogenic twitch contractions of the mouse is olated vas deferens evoked, in the presence of captopril (3 mu M), by electrical field stimulation with trains of 4 rectangular 0.5 ms pulse s of supramaximal strength, delivered at a frequency of 10 Hz every 20 s. 2 BK (0.1 - 300 nM) induced a graded potentiation of twitches, wit h an EC(50) (geometric mean and 95% confidence limits) of 4.5 nM (1.7- 11.6) and an E(max) of 315 +/- 19 mg per 10 mg of wet tissue (n = 6). Similar results were obtained in tissues challenged with Lys-BK, [Hyp( 3)]-BK, Met,Lys-BK and the selective Bz receptor agonist [Tyr(Me)8]-BK (0.1-300 nM). 3 The selective B-2 receptor antagonists, Hoe 140 (1-10 nM) and NPC 17731 (3-30 nM), caused graded rightward shifts df the cu rve to BK-induced twitch potentiation, yielding apparent pA(2) values of 9.65 +/- 0.09 and 9.08 +/- 0.13, respectively, and Schild plot slop es not different from 1. Both antagonists (100 nM) failed to modify si milar twitch potentiations induced by substance P (3 nM) or endothelin -1 (1 nM). Preincubation with the selective B-1 receptor antagonist, [ Leu(8),des-Arg(9)]-BK (1 mu M), increased the potentiating effect of B K on twitches at 30-300 nM. 4 In contrast to BK, the selective B-1 rec eptor agonist, [des-Arg(9)]-BK (0.3-1000 nM) reduced the amplitude of twitches in a graded fashion, with an IC50 of 13.7 nM (10.4-16.1) and an I-max of 175 +/- 11 mg (n = 4). The twitch depression induced by [d es-Arg(9)]-BK (300 nM) was not affected by Hoe 140 (30 nM) or NPC 1773 1 (100 nM), but was abolished by the selective B-1 receptor antagonist , [Leu(8),des-Arg(9)]-BK (1 mu M), which did not modify the twitch inh ibitory effect of clonidine (1 nM) or morphine (300 nM). 5 In non-stim ulated preparations, BK (100 nM) also potentiated, in a Hoe 140-sensit ive (10 nM) manner, the contractions induced by ATP (100 mu M), but no t by noradrenaline (10 mu M), whereas [des-Arg(9)]-BK (300 nM) did not modify the contractions induced by either agonist. 6 It is concluded that the mouse vas deferens expresses both B-1 and B-2 receptors, whic h modulate sympathetic neurotransmission in opposing ways. Neurogenic contractions are inhibited by stimulation of possibly prejunctional B- 1 receptors, whereas activation of B-2 receptors increases twitch cont ractions, in part by amplifying the responsiveness of the smooth muscl e cells to the sympathetic co-transmitter ATP.