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  • Title: Acrosomal alkalization triggers Ca2+ release and acrosome reaction in mammalian spermatozoa.
    Author: Chávez JC, De la Vega-Beltrán JL, José O, Torres P, Nishigaki T, Treviño CL, Darszon A.
    Journal: J Cell Physiol; 2018 Jun; 233(6):4735-4747. PubMed ID: 29135027.
    Abstract:
    The sperm acrosome reaction (AR), an essential event for mammalian fertilization, involves Ca2+ permeability changes leading to exocytosis of the acrosomal vesicle. The acrosome, an intracellular Ca2+ store whose luminal pH is acidic, contains hydrolytic enzymes. It is known that acrosomal pH (pHacr ) increases during capacitation and this correlates with spontaneous AR. Some AR inducers increase intracellular Ca2+ concentration ([Ca2+ ]i ) through Ca2+ release from internal stores, mainly the acrosome. Catsper, a sperm specific Ca2+ channel, has been suggested to participate in the AR. Curiously, Mibefradil and NNC55-0396, two CatSper blockers, themselves elevate [Ca2+ ]i by unknown mechanisms. Here we show that these compounds, as other weak bases, can elevate pHacr , trigger Ca2+ release from the acrosome, and induce the AR in both mouse and human sperm. To our surprise, μM concentrations of NNC55-0396 induced AR even in nominally Ca2+ free media. Our findings suggest that alkalization of the acrosome is critical step for Ca2+ release from the acrosome that leads to the acrosome reaction.
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