In vivo potentiation of muscle torque is enhanced in female mice through estradiol-estrogen receptor signaling

Estradiol affects several properties of skeletal muscle in females including strength. Here, we developed an approach to measure in vivo posttetanic twitch potentiation (PTP) of the anterior crural muscles of anesthetized mice and tested the hypothesis that 17b-estradiol (E₂) enhances PTP through estrogen receptor (ER) signaling. Peak torques of potentiated twitches were 40%–60% greater than those of unpotentiated twitches and such PTP was greater in ovary-intact mice, or ovariectomized (Ovx) mice treated with E_2, compared with Ovx mice (P 0.047). PTP did not differ between mice with and without ERa ablated in skeletal muscle fibers (P = 0.347). Treatment of ovary-intact and Ovx mice with ERb antagonist and agonist (PHTPP and DPN, respectively) did not affect PTP (P 0.258). Treatment with G1, an agonist of the G protein-coupled estrogen receptor (GPER), significantly increased PTP in Ovx mice from 41 ± 10% to 66 ± 21% (means ± SD; P = 0.034). Collectively, these data indicate that E₂ signals through GPER, and not ERa or ERb, in skeletal muscles of female mice to augment an in vivo parameter of strength, namely, PTP.