Calcium flux and membrane potential hyperpolarization observed during prolonged sperm storage in the Mexican big eared bat Corynorhinus mexicanus

Mammalian sperm capacitation includes biochemical and physiological changes, such as (Ca2+)i increase, hyperpolarization of the plasma membrane potential, and sperm hyperactivation, among others. These changes provide the sperm the ability to fertilize. In the bat Corynorhinus mexicanus, there is an asynchrony between spermatogenesis and sperm storage in males, with the receptivity of the female. For instance, in C. mexicanus spermatogenesis occurs before the reproductive season. During the reproductive period, the sperm are stored in the epididymis for few months and the testis undergoes a regression, indicating low or almost null sperm production. Therefore, it is unclear if the required elements necessary to sperm fertilization success undergoes maturation or preparation during epididymis storage. Here, we characterized a pH-sensitive motility hyperactivation and a Ca2+ influx in sperm which was regulated by alkalinization and progesterone. In addition, by electrophysiological recordings we registered currents that were stimulated by alkalinization and inhibited by RU1968 (a specific CatSper inhibitor), strongly suggesting that these currents were evoked via CatSper, a sperm Ca2+ specific channel indispensable for mammalian fertilization. We also found a hyperpolarization of the membrane potential, such as in other mammalian species, that increased according to the month of capture, reaching the biggest hyperpolarization during the mating season. In conclusion, our results suggest that C. mexicanus sperm have a functional CatSper and undergoes a capacitation-like process such as other mammals, particularly a Ca2+ influx and a membrane potential hyperpolarization.