An adhesion-associated agonist from the zona pellucida activates G protein-promoted elevations of internal Ca2+ and pH that mediate mammalian sperm acrosomal exocytosis.
Solubilized oocyte zonae pellucidae promoted acrosomal exocytosis in fura-2- or carboxyfluorescein-loaded, mature bovine sperm. Associated elevations of internal [Ca2+] and pH in sperm suspensions were first detectable at 2-5 min, without apparent temporal resolution, and increased monotonically thereafter. Video imaging of fura-2-loaded, single cells identified a responsive subpopulation, destined to undergo exocytosis, that displayed no early transient but manifested lags of 1-7 min then sustained elevations of internal [Ca2+]. Both the zona-induced exocytosis and dye responses were diminished for functionally immature sperm and for mature sperm treated preliminarily with pertussis toxin. Together, these results indicate that a developmentally regulated mechanism of signal transduction employs G protein(s) to couple the physiological (zona) agonist to alterations of the internal ionic mediators of acrosomal exocytosis.
Florman
H M
HM
Department of Meat and Animal Science, University of Wisconsin, Madison 53706.
Tombes
R M
RM
First
N L
NL
Babcock
D F
DF
D000177:Acrosome / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000502:physiology; D002417:Cattle; D002448:Cell Adhesion; D002451:Cell Compartmentation; D003593:Cytoplasm / Q000502:physiology; D005089:Exocytosis / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D008297:Male; D010063:Ovum / Q000502:physiology*; D037342:Pertussis Toxin; D012995:Solubility; D013094:Spermatozoa / Q000502:physiology*; D014741:Video Recording; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D015044:Zona Pellucida / Q000502:physiology*
D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D002118:Calcium