Developmental changes in contraction of gastric smooth muscle cells in rats correlate with their differences in RhoA/ROCK pathway

Previous research has shown that smooth muscle of the stomach undergoes developmental changes in the intracellular regulatory mechanism responsible for the contractile process. Whether these developmental changes relate to differences in the expression and/or activity of the key enzymes regulating smooth muscle contraction has not been previously evaluated. Therefore, we aimed to examine the expression and activation of the small monomeric G protein "RhoA" and Rho kinase (ROCK) as well as their correlation with the contraction of gastric smooth muscle cells (GSMCs) in newborn vs. adult rats. Freshly isolated single GSMCs from Sprague-Dawley rats at 1 week (newborn) and 3 months (adult) of age were used in the study. Protein and mRNA expression levels of both ROCK2 and total RhoA were higher in adult compared to newborn rats. Moreover, acetylcholine (ACh)-induced contractions of GSMCs in adult rats were significantly higher than that in newborn animals. Meanwhile, ROCK and Rho activation was higher in adult stomach cells compared to newborn ones. Pretreatment of GSMCs with Y-27632, the ROCK inhibitor, significantly reduced ACh-induced contraction in both groups of cells and greatly abolished contractile differences. In conclusion, our results indicate that RhoA/ROCK pathway and contraction of stomach muscle cells are under developmental regulation.