A sustained increase in intracellular Ca(2+) is required for the acrosome reaction in sea urchin sperm.
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.
González-Martínez
M T
MT
Departamento de Genética y Fisiología Molecular del Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca, Morelos 62271, Mexico.
Galindo
B E
BE
de De La Torre
L
L
Zapata
O
O
Rodríguez
E
E
Florman
H M
HM
Darszon
A
A
D020101:Acrosome Reaction; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005306:Fertilization; D006863:Hydrogen-Ion Concentration; D007211:Indoles / Q000494:pharmacology; D008297:Male; D008954:Models, Biological; D009532:Nickel / Q000494:pharmacology; D012617:Sea Urchins; D012623:Seawater; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors
D015220:Calcium Channels; D004791:Enzyme Inhibitors; D007211:Indoles; D004533:Egtazic Acid; D019284:Thapsigargin; D009532:Nickel; D002118:Calcium; C000543:cyclopiazonic acid