Influence of respiratory tract viral infection on endothelin-1-induced potentiation of cholinergic nerve-mediated contraction in mouse trachea

1 This study examined the influence of respiratory tract infection with influenza A/PR-8/34 virus on endothelin receptor-mediated modulation of contraction induced by stimulation of cholinergic nerves in mouse isolated trachea. 2 The ET(B) receptor-selective agonist, sarafotoxin S6c (30 nM) induced large transient contractions (118 +/- 5% C-max, n = 13; where C-max is the contraction induced by 10 mu M carbachol) of isolated tracheal segments from control mice. The peak contractile response to 30 nM sarafotoxin S6c was significantly lower in preparations from virus-inoculated mice at day 2 (57 +/- 8% C-max, n = 3, P<0.05) and 4 postinoculation (90 +/- 8% C-max, n = 9, P<0.05), consistent with virus-induced attentuation of the ET(B) receptor-effector system linked to airway smooth muscle contraction. The mean peak contraction to 30 nM sarafotoxin S6c of preparations from virus-inoculated mice at day 8 post-inoculation (94 +/- 17% C-max, n = 4) was not significantly different from that of control. 3 Electrical held stimulation (EFS; 90 V, 0.5 ms duration, 10 s train, 0.1-30 Hz) of preparations from control and virus-inoculated mice, caused contractions that were abolished by 0.1 mu M atropine or 3 mu M tetrodotoxin, indicating that these responses were mediated by neuronally released acetylcholine. Sarafotoxin S6c markedly potentiated contractions induced by a standard stimulus (0.3 Hz, every 3 min) in tracheal segments from control and virus-inoculated mice. In tracheal tissue from control mice, 30 nM sarafotoxin S6c significantly increased a standard EFS-induced contraction of 24 +/- 4% C-max by a further 24 +/- 3% C-max (i.e. 2 fold increase, n = 11). Sarafotoxin S6c (30 nM) also markedly potentiated standard EFS-induced contractions in preparations from virus-inoculated mice at day 2 (17 +/- 2% C-max, n = 3), day 4 (17 +/- 5% C-max, n = 9) and day 8 (26 +/- 5% C-max, n = 4) post-inoculation. The level of potentiation of EFS-induced contractions in preparations from virus-inoculated mice was similar to that in tissue from control mice at days, 2, 4 and 8 post-inoculation. In contrast, sarafotoxin S6c (30 nM) did not enhance contractile responses of tracheal segments from control and virus-inoculated mice to exogenously applied acetylcholine (n = 3). 4 Endothelin-1 (1 nM) caused similar potentiations of standard EFS-induced contractions in tracheal segments from control (13 +/- 2% C-max, n = 23) and virus-inoculated mice at day 2 (13 +/- 1% C-max, n = 5), day 4 (16 +/- 5% C-max, n = 6), and day 8 (13 +/- 3% C-max, n = 8) post-inoculation. In contrast, 1 nM endothelin-1 did not enhance contractile responses of tracheal segments from control and virus-inoculated mice to exogenously applied acetylcholine (n = 4). Neither the ET(A) receptor-selective antagonist, BQ-123 (3 mu M) nor the ET(B) receptor-selective antagonist, BQ-788 (1 mu M) alone had any significant inhibitory effect on endothelin-1-induced potentiations of tracheal segments from control or virus-inoculated mice at days 2, 4 and 8 post-inoculation. However, simultaneous pre-incubation with BQ-123 (3 mu M) and BQ-788 (1 mu M) prevented endothelin-1-evoked potentiations, indicative of a role for both ET(A) and ET(B) receptors in this system. 5 These data clearly demonstrate that respiratory tract viral infection attenuated the function of the postjunctional ET(B) receptor-effector system linked directly to airway smooth muscle contraction. However, the function of prejunctional ET(A) and ET(B) receptor-effector systems linked to augmentation of cholinergic nerve-mediated airway smooth muscle contraction remained unaffected during respiratory tract viral infection in mice.