Characterization of nicotinic cholinergic receptors

Objective: To characterize nicotinic cholinergic receptors (cholinoceptors) in frog rectus abdominis and mouse esophagus. Material and Methods: Isolated preparations of mouse esophagus and frog rectus abdominis were separately mounted in organ baths filled with Krebs and Ringer solutions respectively. The organ bath medium was continuously gassed with 95% O2 and 5% CO2 and the temperature was maintained at 370C and 250C for mouse esophagus and frog rectus abdominis respectively. Changes in muscle length were recorded by isotonic transducers. The effects of neuromuscular blocking agents were investigated on contractions mediated by nicotinic cholinoceptors in both the preparations. Results: The contractions induced by carbachol (Cch) (5x10-6-5x10-5 M) were significantly inhibited by pancuronium (10-9-5x10-8) in mouse esophagus and frog rectus abdominis. Gallamine inhibited the contractions in the frog rectus abdominis but it failed to reduce the Cch responses in the mouse esophagus. On the other hand, d-tubocurarine caused irreversible contractions in the basal tonus of frog rectus abdominis, but it reduced the contractions evoked by Cch in mouse esophagus. Conclusion: The different effects of the neuromuscular blocking agents on contractions mediated by nicotinic cholinoceptors in frog rectus abdominis and mouse esophagus indicated that the nicotinic cholinoceptors in two different tissues may not be identical and these differences may be attributed to the different nicotinic cholinoceptor subtypes.