Reversible stress softening in layered rat esophagus in vitro after potassium chloride activation

Abstract

Significant stress softening recovery after potassium chloride (KCl) administration was previously demonstrated in the intact rat esophageal wall. The aim of this study is to investigate the effect of KCl activation on stress softening recovery in the separated mucosa–submucosa layer and muscle layer of rat esophagus. Three series of loading–unloading distensions were carried out on 10 rat esophagi where the two separated layers were distended at luminal pressure levels 0.5, 1.0 and 2.0 kPa. Numerous distension cycles were done in $\hbox {Ca}^{2+}$-free Krebs solution before and after activation with KCl (110 mmol) for 3 min in calcium-containing media. The diameter and luminal pressure were recorded for stress and strain calculation. During KCl activation, the muscle layer responded with a high-amplitude contraction, and the mucosa–submucosa layer responded with a longer-lasting low-amplitude contraction. The hysteresis loop areas from the muscle layer were significantly bigger than those from the mucosa–submucosa layer at distension pressures 1.0 and 2.0 kPa (${F}>4.9, {p}<0.001$). The calculated stiffness in the mucosa–submucosa layer was significantly higher than that in the muscle layer (${p}<0.001$). After activation with KCl, the stored energy and the stiffness after the stress and viscoelasticity softening increased in both layers, indicating that the reversible stress softening in esophagus after KCl activation is existed in both layers.