Contractile properties of esophageal striated muscle: comparison with cardiac and skeletal muscles in rats

Abstract

The external muscle layer of the mammalian esophagus consists of striated muscles. We investigated the contractile properties of esophageal striated muscle by comparison with those of skeletal and cardiac muscles. Electrical field stimulation with single pulses evoked twitch-like contractile responses in esophageal muscle, similar to those in skeletal muscle in duration and similar to those in cardiac muscle in amplitude. The contractions of esophageal muscle were not affected by an inhibitor of gap junctions. Contractile responses induced by high potassium or caffeine in esophageal muscle were analogous to those in skeletal muscle. High-frequency stimulation induced a transient summation of contractions followed by sustained contractions with amplitudes similar to those of twitch-like contractions, although a large summation was observed in skeletal muscle. The results demonstrate that esophageal muscle has properties similar but not identical to those of skeletal muscle and that some specific properties may be beneficial for esophageal peristalsis.

Figure 1

Single-pulse electrical stimulation-induced twitch-like contractions of esophageal, skeletal, and cardiac muscles in rats. (a) Representative traces of the contractile responses to electrical field stimulations (EFS) in esophageal, skeletal, and cardiac muscle preparations are shown. EFS was applied by using single pulses (voltage: 80 V, duration: 10 ms). Closed circles indicate the points of EFS. (b) Summary graphs of the duration of the EFS-evoked twitch-like contractions in esophageal (n = 16), skeletal (n = 6), and cardiac (n = 5) muscle preparations. Each bar represents the mean ± S.D. **  shows significant difference (P < .01). NS shows no significant difference.

Figure 2

Multipulse electrical stimulation-induced contractile responses of esophageal, skeletal, and cardiac muscles. Representative traces of the contractile responses to single and multipulse repeated EFS in esophageal (a), skeletal (b), and cardiac (c) muscle preparations are shown. Similar results were reproducibly obtained in five independent experiments. EFS was applied by using single or repeated pulses (80 V-10 ms, 20 Hz for 1 s). Closed circles and underbars indicate the points of single EFS and the location of multiple EFS, respectively.

Figure 3

Effects of halothane on the contractile responses in esophageal and cardiac muscles. Single-pulse EFS was applied in the absence and presence of halothane (50 mM), an inhibitor of gap junctions, and the contractile responses were recorded. Representative traces of esophageal (a) and cardiac (b) muscle preparations are shown. Similar results were reproducibly obtained in four independent experiments.

Figure 4

Contractile responses induced by high potassium or caffeine in esophageal, skeletal, and cardiac muscles. Muscle preparations were stimulated with high potassium (a) or caffeine (b). Representative traces of the contractile responses in esophageal, skeletal and cardiac preparations are shown. Similar results were reproducibly obtained in five independent experiments. Underbars indicate the application of high potassium (118.4 mM) and caffeine (20 mM).