Epithelium- and mucosa-dependent relaxation and contraction of normal equine trachealis muscle in vitro.

The research article investigates how the removal of the epithelium and mucosa affects the relaxation and contraction of normal equine trachealis muscle in vitro.

Research Method and Tools

The researchers dissected strips of trachealis muscle from the mid-cervical part of the trachea of horses without respiratory diseases. These tissues were classified into two groups: with epithelium and mucosa intact, and with them removed. These tissues were submerged in a bath filled with Krebs-bicarbonate solution, kept at 37 degrees C, and aerated with 5% CO2 in oxygen. The tension was recorded continuously.

• Thee contractile response was observed by applying square-wave electrical stimulations of varying frequency, voltage, and pulse duration.
• Various substances such as Atropine and Acetylcholine were added to the bath to observe their impact on the contraction of tissues.
• Isoproterenol was used to trigger relaxation in tissues pre-contracted with Acetylcholine.

Findings

The magnitude of isometric tension depended on the frequency, voltage, and pulse duration of the electrical stimulations. A stimulus of 18 V, 20 Hz, and 0.5 ms induced maximum contraction. The research found that adding Atropine eliminated the response to 18 V and 0.5 ms at all frequencies, indicating that it inhibited the contraction.

• Acetylcholine, when added in increasing concentrations, resulted in a concentration-dependent increase in isometric tension.
• When Isoproterenol was introduced to the tissues previously contracted with Acetylcholine, it caused a decrease in isometric tension in a concentration-dependent manner.
• The study also observed that the presence or absence of the epithelium and mucosa affected the contraction and relaxation curves.
• The contractile response to Acetylcholine was increased in tissues without epithelium and mucosa, specifically at bath concentrations of 3.1 x 10(-7) M and 10(-6) M.

Conclusion

The findings suggest that the presence of the epithelium and mucosa enhances the intensity of relaxations induced by Isoproterenol. Although the contraction and relaxation patterns were qualitatively similar for tissues with and without epithelium and mucosa, there were quantitative differences as the contraction and relaxation responses varied with the presence or absence of these structures.