A sustained increase in intracellular Ca(2+) is required for the acrosome reaction in sea urchin sperm. |
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Authors: | M T González-Martínez B E Galindo L de De La Torre O Zapata E Rodríguez H M Florman A Darszon |
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Institution: | Departamento de Genética y Fisiología Molecular del Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62271, Mexico. |
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Abstract: | The acrosome reaction (AR), necessary for fertilization in many species, requires an increase in intracellular Ca(2+) (Ca(2+)](i)). In sea urchin sperm, the AR is triggered by an egg-jelly factor: the associated Ca(2+)](i) elevation lasts minutes and involves two Ca(2+) permeable channels. Both the opening of the second channel and the onset of the AR occur approximately 5 s after treatment with egg factor, suggesting that these events are linked. In agreement, removal of Ca(2+) from sea water or addition of Ca(2+) channel blockers at the time when opening of the second channel is first detected inhibits AR and causes a "rapid" (t(1/2) = 3--15 s) decrease in Ca(2+)](i) and partial inhibition of the intracellular pH change associated with the AR. Simultaneous addition of NH(4)Cl and either EGTA, Co(2+), or Ni(2+) 5 s after egg factor prevents the partial inhibition of the evoked pH(i) change observed but does not reverse AR inhibition. Therefore, the sustained increase in Ca(2+)](i) caused by the second Ca(2+) channel is needed for the sperm AR. Experiments with agents that induce capacitative Ca(2+) uptake (thapsigargin and cyclopiazonic acid) suggest that the second channel opened during the AR could be a store-operated Ca(2+) channel. |
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