A Sustained Increase in Intracellular Ca2+ Is Required for the Acrosome Reaction in Sea Urchin Sperm

• Published in: Developmental biology 2001-08, Vol.236 (1), p.220-229
• Main Authors: González-Martínez, Marco T., Galindo, Blanca E., de De La Torre, Lucia, Zapata, Otilia, Rodríguez, Esmeralda, Florman, Harvey M., Darszon, Alberto
• Format: Article
• Language: English
• Subjects: Ca2+ channels; sperm; store-operated channels
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1006/dbio.2001.0323

The acrosome reaction (AR), necessary for fertilization in many species, requires an increase in intracellular Ca2+ ([Ca2+]i). In sea urchin sperm, the AR is triggered by an egg-jelly factor: the associated [Ca2+]i elevation lasts minutes and involves two Ca2+ permeable channels. Both the opening of the second channel and the onset of the AR occur ∼5 s after treatment with egg factor, suggesting that these events are linked. In agreement, removal of Ca2+ from sea water or addition of Ca2+ channel blockers at the time when opening of the second channel is first detected inhibits AR and causes a “rapid” (t1/2 = 3–15 s) decrease in [Ca2+]i and partial inhibition of the intracellular pH change associated with the AR. Simultaneous addition of NH4Cl and either EGTA, Co2+, or Ni2+ 5 s after egg factor prevents the partial inhibition of the evoked pHi change observed but does not reverse AR inhibition. Therefore, the sustained increase in [Ca2+]i caused by the second Ca2+ channel is needed for the sperm AR. Experiments with agents that induce capacitative Ca2+ uptake (thapsigargin and cyclopiazonic acid) suggest that the second channel opened during the AR could be a store-operated Ca2+ channel.