Evidence of poor conduction of muscle excitation in the longitudinal axis of guinea-pig isolated trachea.

1 Mechanical activity was recorded from one segment of guinea-pig trachealis muscle while intracellular electrical activity was simultaneously recorded from a contiguous segment. When the tissue was stimulated by 1-32 mmol/l tetraethylammonium (TEA) it became clear that the electrical and mechanical records were not directly correlated. 2 Dual recording of mechanical activity from two contiguous segments of trachealis revealed that one tissue segment could exhibit phasic activity whilst the other could exhibit tonic activity, despite exposure to the same concentration of TEA. 3 Histological studies revealed that the trachealis muscle was organized into bundles largely separated from one another by spaces filled with connective tissue. However, muscle bundles branched and formed anastomotic connections with near neighbours. 4 It is concluded that the cell to cell spread of muscle excitation is very poor along the longitudinal axis of the trachea. The trachealis muscle as a whole does not function as a single unit. Rather it may represent a series of effector units each comprising a small number of smooth muscle bundles.