title: Ion channel activity of membrane vesicles released from sea urchin sperm during the acrosome reaction.
abstract: The sperm acrosome reaction (AR) involves ion channel activation. In sea urchin sperm, the AR requires Ca2+ and Na+ influx and K+ and H+ efflux. During the AR, the plasma membrane fuses with the acrosomal vesicle membrane forming hybrid membrane vesicles that are released from sperm into the medium. This paper reports the isolation and preliminary characterization of these acrosome reaction vesicles (ARVs), using synaptosome-associated protein of 25 kDa (SNAP-25) as a marker. Isolated ARVs have a unique protein composition. The exocytosis regulatory proteins vesicle-associated membrane protein and SNAP-25 are inside ARVs, as judged by protease protection experiments, and membrane associated based on Triton X-114 partitioning. ARVs fused with planar bilayers display three main types of single channel activity. The most frequently recorded channel is cationic, weakly voltage dependent and has a low open probability that increases with negative potentials. This channel is activated by cAMP, blocked by Ba2+, and has a PK+/PNa+ selectivity of 4.5. ARVs represent a novel membrane preparation suitable to deepen our understanding of ion channel activity in the AR and during fertilization.
authors.affiliation: Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, USA.
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Schulz
authors.forename: Jose L
authors.initials: JL
authors.lastname: De la Vega-Beltrán
authors.forename: Carmen
authors.initials: C
authors.lastname: Beltrán
authors.forename: Victor D
authors.initials: VD
authors.lastname: Vacquier
authors.forename: Alberto
authors.initials: A
authors.lastname: Darszon
mesh_terms: D020101:Acrosome Reaction / Q000502:physiology*; D000818:Animals; D015415:Biomarkers / Q000032:analysis; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008051:Lipid Bilayers; D008297:Male; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000032:analysis; D009419:Nerve Tissue Proteins / Q000032:analysis; D010539:Permeability; D011188:Potassium / Q000378:metabolism; D012617:Sea Urchins; D012964:Sodium / Q000378:metabolism; D013094:Spermatozoa / Q000502:physiology*; D050825:Synaptosomal-Associated Protein 25
chemical_list: D015415:Biomarkers; D007473:Ion Channels; D008051:Lipid Bilayers; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D050825:Synaptosomal-Associated Protein 25; D012964:Sodium; D000242:Cyclic AMP; D011188:Potassium