Ionic Channels in the Plasma Membrane of Sea Urchin Sperm
The exchange of information between a cell and its environment is frequently mediated by ionic movements through the plasma membrane. The physiology of sea urchin sperm is a representative case in which this phenomenon occurs. For instance, when these cells are spawned into sea water, their motility and respiration activate (Ohtake, 1976; Nishioka and Cross, 1978; Christen et al., 1982). This activation is mostly dependent on the transport of Na+ and H+ through the plasma membrane (Nishioka and Cross, 1978). The sperm acrosome reaction, a prerequisite for egg fertilization, is also modulated by ionic fluxes (Schakmann et al., 1978). This reaction in sea urchin sperm consists of the exocytosis of the acrosomal vesicle located at the anterior region of the sperm head (Dan, 1952; Summers et al., 1975) and leads to the exposure of a protein required for sperm-egg binding (Vacquier and Moy, 1977; Glabe and Lennarz, 1979) and of lytic enzymes that digest the coat of the egg (Levine and Walsh, 1979; Green and Summers, 1980). Also during the process, the intracellular cyclic nucleotides increase (Garbers and Kopf, 1980), and an actin-containing acrosomal tubule is formed (Tilney et al., 1973).
KeywordsAcrosome Reaction Sperm Head Sperm Membrane Sperm Plasma Membrane Jelly Coat
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