Store-operated calcium channels trigger exocytosis of the sea urchin sperm acrosomal vesicle.
The acrosome reaction (AR) of sperm is a prerequisite for fusion with the egg. In sea urchins, the complete AR (CAR) consists of exocytosis of the acrosomal vesicle (AV) and polymerization of acrosomal actin to form the approximately 1 micro m long acrosomal process. The fucose sulfate polymer (FSP) of egg jelly stimulates Ca(2+) entry through two distinct Ca(2+) channels and induces the CAR. Here we report that the second channel is blocked by SKF96365 (SKF), an inhibitor of store-operated channels. SKF also blocks the thapsigargin (TG), trifluoperazine (TFP), and calmidizolium (CMZ) stimulated Ca(2+) entry into sperm. These data indicate that the second Ca(2+) channel is a store-operated channel (SOC) that may be regulated by calmodulin. The TG, TFP, and CMZ-induced intracellular Ca(2+) elevations are similar to those induced by FSP, but the sperm acrosomal process does not polymerize. An antibody to bindin, the major protein of the AV, showed that in a significant percentage of these drug-treated sperm, the AV had undergone exocytosis. When NH(4)Cl was added to increase intracellular pH, the TG-treated sperm polymerized actin to form the acrosomal process. We conclude that the second Ca(2+) channel of sea urchin sperm is a SOC that triggers AV exocytosis.
Hirohashi
Noritaka
N
Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0202, USA. vvacquier@ucsd.edu
Vacquier
Victor D
VD
D000177:Acrosome / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D020101:Acrosome Reaction / Q000187:drug effects; D000199:Actins / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000032:analysis; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D005089:Exocytosis; D005643:Fucose / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D012617:Sea Urchins; D022142:Secretory Vesicles / Q000502:physiology*; D013464:Sulfuric Acids / Q000037:antagonists & inhibitors; D019284:Thapsigargin / Q000494:pharmacology
D000199:Actins; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007093:Imidazoles; D013464:Sulfuric Acids; C061711:fucose-sulfate glycoconjugate; D005643:Fucose; D019284:Thapsigargin; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium