Aim: 

Vertebrate nonmuscle myosin II have been shown to play important roles in a variety of cellular processes. The aim of the present work was to address the role of myosin II in the cell volume homeostasis at the epithelial level.

Methods: 

The study was carried out on a model salt transport epithelium, the intestine of European eel, which is able to perform a Regulatory Volume Increase accounted by the stimulation of the luminal Na+-K+-2Cl- cotransporter following an hypertonic stress. Short circuit current measurements and confocal laser scanning microscopy were applied.

Results: 

The hypertonicity induced stimulation of Na+-K+-2Cl- was sensitive to bebblistatin, specific inhibitor of myosin II, and ML-7, inhibitor of myosin light chain kinase, suggesting its dependence from myosin-driven mechanisms. It was also sensitive to Rho family small GTPases and ROK, known regulators of myosin II phosphorylation. Moreover, the process was also sensitive to p38 MAPK and c-JNK but not ERK1/2 inhibition. A specific myosin labelling was observed as immunofluorescence spots associated to the cortical F-actin cytoskeleton at the junctional level. Hypertonicity increased myosin II spots thickness was sensitive to Clostridium difficile toxin B.

Conclusion: 

Myosin II recruitment to the junctional region and a myosin dependent upregulation of Na+-K+-2Cl-, both dependent on small Rho GTPase, could be the expression of the multiple roles of myosin II in the response of the epithelium to hypertonicity.