The Effects of Estrogen on Cytoplasmic Ca²+ Concentration of Masticatory Muscles Myoblast in Acid Condition

Temporomandibular disorders (TMD) affect women with a higher frequency than men, which suggests a possible link between its pathogenesis and sex hormone, such as estrogen. Cytoplasmic Ca²⁺ plays an important role in cell normal function and cytoplasmic Ca²⁺ accumulation may be a key factor that causes skeletal muscle fatigue and injury. To investigate the effects of estrogen on intracellular Ca²⁺ concentration of masticatory muscles, myoblasts from masticatory muscles of female Sprague-Dawley rats were cultured and loaded with Fluo-4 AM, the indicator of Ca²⁺. And the dynamic Ca²⁺ transients were visualized with confocal laser-scanning microscopy. 17β-estradiol was added to the myoblasts in resting and acid condition (PH=6.7). In the resting condition, 17β-estradiol with the concentration of 10^-9mol/L, 10^-8 mol/L and 10^-7mol/L lead cytoplasmic Ca²⁺ concentration to increase immediately, followed by decreasing right away, and in the end came into a Ca²⁺ homeostasis similar with the concentration at base line. In the acid condition (PH=6.7) which mimicked muscle fatigue state, 17β-estradiol with the concentration of 10^-9mol/L 10^-8mol/L and 10^-7mol/L induced the cytoplasmic Ca²⁺ concentration to decrease immediately, then came into a new Ca²⁺ homeostasis which was lower than the concentration at base line. The results suggest that in acid condition, estrogen may maintain the skeletal cytoplasmic Ca²⁺ concentration in a lower level and reduce the cytoplasmic Ca²⁺ accumulation to keep the normal functions of masticatory muscles myoblasts.