Gender differences in the regulation of MLC phosphorylation and smooth muscle contraction in rat stomach.

Evidence of sex-related differences in gastrointestinal (GI) functions has been reported in the literature. In addition, various GI disorders have disproportionate prevalence between the sexes. An essential step in the initiation of smooth muscle contraction is the phosphorylation of the 20-kDa regulatory myosin light chain (MLC) by the Ca/calmodulin-dependent myosin light chain kinase (MLCK). However, whether male stomach smooth muscle inherits different contractile signaling mechanisms for the regulation of MLC phosphorylation from that in females has not been established. The present study was designed to investigate sex-associated differences in the regulation of MLC phosphorylation and thus muscle contraction in gastric smooth muscle cells (GSMCs). Experiments were performed on GSMCs freshly isolated from male and female rats. Contraction of the GSMCs in response to acetylcholine (ACh), a muscarinic agonist, was measured via scanning micrometry in the presence or absence of the MLCK inhibitor, ML-7. Additionally, the protein levels of MLC, MLCK and phosphorylated MLC were measured by ELISA. The protein levels of MLC and MLCK were indifferent between the sexes. ACh induced greater contraction (P<0.05) as well as greater MLC phosphorylation (P<0.05) in male GSMCs compared with female. Pretreatment of GSMCs with ML-7 significantly reduced the ACh-induced contraction (P<0.05) and MLC phosphorylation (P<0.05) in the male and female cells, and notably, abolished the contractile differences between the sexes. In conclusion, MLC phosphorylation and thus muscle contraction may be activated to a greater extent in male rat stomach compared with that in females.