Maitotoxin potently promotes Ca 2+ influx in mouse spermatogenic cells and sperm, and induces the acrosome reaction

Maitotoxin (MTX), a potent marine toxin, activates Ca 2+ entry via nonselective cation channels in a wide variety of cells. The identity of the channels involved in MTX action remains unknown. In mammalian sperm, Ca 2+ entry through store‐operated channels regulates a number of physiological events including the acrosome reaction (AR). Here we report that MTX produced an increase in the intracellular concentration of Ca 2+ ([Ca 2+ ] i ) in spermatogenic cells that depended on extracellular Ca 2+ . Ni 2+ and SKF96365 diminished the MTX‐activated Ca 2+ uptake, at concentrations they inhibit store‐operated channels, and in a similar manner as they inhibit the Ca 2+ influx activated following depletion of intracellular stores by thapsigargin (Tpg). In addition, MTX significantly increased [Ca 2+ ] i in single mature sperm and effectively induced the AR with a half‐maximal concentration (ED 50 ) of ∼1.1 nM. Notably, SKF96365 similarly inhibited the MTX‐induced increase in sperm [Ca 2+ ] i and the AR triggered by the toxin, Tpg and zona pellucida . These results suggest that putative MTX‐activated channels may be involved in the Ca 2+ influx required for mouse sperm AR. J. Cell. Physiol. 206: 449–456, 2006. © 2005 Wiley‐Liss, Inc.