Autoregulation of @entity934 release from vagus nerve terminals through activation of muscarinic receptors in the @entity235 XXXX .

@entity825 @entity1169 @entity308 @entity9563 @entity235 @entity969 @entity1617 @entity4140 @entity3352 @entity934
1. The effects of @entity4140 and @entity9563 on the membrane and contractile properties of smooth muscle cells and on excitatory neuro-effector transmission in the @entity235 @entity825 were investigated by means of microelectrode, double @entity969 gap and tension recording methods. 2. @entity4140 (10(-7) M) and @entity9563 (10(-5) M) had no effect on the resting membrane potential or the input resistance of the smooth muscle cells. 3. @entity4140 (10(-10)-10(-9) M) and @entity9563 (10(-7) M) enhanced the amplitude of twitch contractions evoked by field stimulation in the combined presence of @entity3352 (10(-5) M) and @entity1169 (10(-6) M). At higher concentrations @entity4140 (10(-8) M) inhibited the twitch contractions in a dose-dependent manner. Both @entity4140 and @entity9563 in doses over 10(-7) and 10(-5) M, respectively, reduced muscle tone. 4. @entity4140 (10(-10)-10(-9) M) and @entity9563 (10(-7) M) enhanced the amplitude of excitatory junction potentials (e.j.ps) evoked by field stimulation (single or repetitive stimulation). However, a high concentration of @entity4140 (10(-8) M) reduced the amplitude of e.j.ps. In parallel with its action on e.j.ps, @entity4140 (over 10(-9) M) reduced the response of smooth muscle cells to @entity934 ( @entity1617 ), in a dose-dependent manner. @entity9563 (5 X 10(-5) M) markedly enhanced the amplitude of e.j.ps but also reduced the response of muscle cells to @entity1617 . 5. @entity1617 (10(-10)-10(-9) M) inhibited twitch contractions evoked by field stimulation, with a slight increase of resting tension. 6. @entity9563 enhanced the summation of e.j.ps during repetitive field stimulation at a high frequency (20 Hz), but was without effect on the @entity308 phenomena of e.j.ps observed during double stimulus experiments at different time intervals (5-60 s). 7. These results indicate that both @entity4140 and @entity9563 have dual actions on pre- and post-junctional muscarinic receptors in @entity235 tracheal tissue. At low concentrations both agents potentiate excitatory neuro-effector transmission, presumably due to enhancement of release of @entity1617 from vagal nerve terminals through blockade of a negative auto-regulatory process activated by endogenous @entity1617 . At higher concentrations, these agents inhibit the response of smooth muscle cells to @entity1617 through post-junctional muscarinic receptors and relaxation of the muscle tissue occurs.
