Effects of relaxants on electrical and mechanical activities in the guinea-pig tracheal muscle.

In isolated tracheal muscles of the guinea-pig, effects of several relaxants were studied by simultaneously recording the membrane potential and mechanical response. Intracellular recordings showed regular slow waves in most preparations. There was a close correlation between membrane potential and slow wave amplitude. The linear regression line of the slow wave amplitude (Y mV) on the membrane potential (X mV) could be expressed by Y = -0.35X-5.9. The mean values of resting potential and slow wave amplitude were -50.6 +/- 0.6 mV and 11.9 +/- 0.5 mV, respectively. Relaxant drugs used (isoprenaline, terbutaline, adrenaline, noradrenaline, theophylline, forskolin and dibutyryl cyclic AMP) all produced hyperpolarization of the membrane and abolished the slow wave. The degree of relaxation was closely related to these electrical responses, although the recovery of electrical responses was faster than the mechanical response. It was concluded that the relaxation caused by the agents, which are known to increase the intracellular cyclic AMP level, was accompanied by a clear hyperpolarization and suppression of slow waves.