Motility initiation in herring sperm is regulated by reverse sodium-calcium exchange

Abstract

Sperm of the Pacific herring, Clupea pallasi, are unique in that they are immotile upon spawning in the environment. Herring sperm have evolved to remain motionless for up to several days after spawning, yet are still capable of fertilizing eggs. An egg chorion ligand termed ''sperm motility initiation factor'' (SMIF) induces motility in herring sperm and is required for fertilization. In this study, we show that SMIF induces calcium influx, sodium efflux, and a membrane depolarization in herring sperm. Sperm motility initiation by SMIF depended on decreased extracellular sodium (<350 mM) and could be induced in the absence of SMIF in very low sodium seawater. Motility initiation depended on > 1 mM extracellular calcium. Calcium influx caused by SMIF involved both the opening of voltage-gated calcium channels and reverse sodiumcalcium (Na ؉ ͞Ca 2؉ ) exchange. Membrane depolarization was slightly inhibited by a calcium channel blocker and markedly inhibited by a Na ؉ ͞Ca 2؉ exchange inhibitor. Sodium efflux caused by SMIF-initiated motility was observed when using both extracellular and intracellular sodium probes. A Na ؉ ͞Ca 2؉ exchange antigen was shown to be present on the surface of the sperm, primarily over the midpiece, by using an antibody to the canine Na ؉ ͞Ca 2؉ exchanger. This antibody recognized a 120-kDa protein that comigrated with the canine myocyte Na ؉ ͞Ca 2؉ exchanger. Sperm of Pacific herring are now shown to use reverse Na ؉ ͞Ca 2؉ exchange in motility initiation. This mechanism of regulation of motility initiation may have evolved for both maintenance of immotility after spawning as well as ligand-induced motility initiation.T eleost fish sperm are quiescent within the testes and seminal plasma before spawning, but most initiate motility after dilution into the external medium (freshwater or seawater for most species) in which spawning occurs (1). In salmonids, motility initiation occurs with dilution in freshwater, specifically from a reduction in extracellular potassium that drives a membrane hyperpolarization and an increase in intracellular calcium ([Ca 2ϩ ] i ) (2-6). Changes in the concentrations of specific ions (Ca 2ϩ , K ϩ , and possibly Na ϩ and Cl Ϫ ) also have been linked to motility initiation in Atlantic croaker sperm (7). A hyperpolarization of the sperm membrane also has been documented in carp sperm, reportedly linked to the opening of voltage-gated Ca 2ϩ channels and an increase in [Ca 2ϩ ] i (8). In other freshwater teleost sperm (goldfish, zebra fish), as well as in marine teleost sperm (puffer, flounder), motility is believed to occur as a result of nonspecific hypo-or hyperosmotic changes that drive changes in intracellular ion concentrations (5, 9, 10). Thus, in all systems studied to date, a membrane hyperpolarization leads to an increase in [Ca 2ϩ ] i and the initiation of motility.Although the stimulation of sperm motility in the vicinity of eggs has been reported in some teleost fish, only herring sperm have been shown to require an egg chorion-derived ligand for ...

Marine fish spermatozoa: racing ephemeral swimmers

“…In fish, the only clear demonstration is in the pacific herring (Clupea pallasi); spermatozoa are not active when delivered at spawning in SW but only when they happen to reach the egg chorion, more precisely the vicinity of the micropyle (Yanagimachi 1957, Yanagimachi et al 1992, Griffin et al 1996. The motility initiation is regulated by a reverse Na C /Ca 2C exchanger (Vines et al 2002) but some components of the chorion are needed (Oda et al 1995): the herring sperm activating peptide (HSAP) and the sperm motility initiation factor (SMIF). The HSAP has protease inhibitor motifs (Oda et al 1998) which binds to an endopeptidase of the flagellar membrane (Yoshida et al 1999).…”

Asterosap, an Egg Jelly Peptide, Elevate Intracellular Ca²⁺ and Activate the Motility of Spermatozoa

“…Motility of herring spermatozoa initiate when they bind a factor released from eggs. This initiation depends on a NCX that brings Ca 2+ into the spermatozoa in exchange for Na + efflux (Vines et al, 2002).…”

Transmembrane Cell Signaling for the Initiation of Trout Sperm Motility: Roles of Ion Channels and Membrane Hyperpolarization for Cyclic AMP Synthesis

“…It possesses two PKA sites and a His-rich region in the cytoplasmic loop, suggesting regulation of the channel by cAMP-dependent phosphorylation and metal binding. When herring sperm initiate motility upon reception of the 105-kDa glycoprotein, SMIF, membrane hyperpolarization occurs and subsequently both voltagedependent Ca 2+ channels and Na + /Ca 2+ exchangers appear to be activated for Ca 2+ influx (Vines et al, 2002). In this case, the activity of the Na + /Ca 2+ exchanger should operate in reverse.…”

“…Two proteins that activate sperm motility have been identified in herring: one has a small molecular mass (~8 kDa) (Oda et al, 1998), while the other is a 105-kDa glycoprotein present on the micropyle of the egg (Vines et al, 2002). Receptors for these two proteins have not been identified.…”

“…In this case, the activity of the Na + /Ca 2+ exchanger should operate in reverse. A putative 120-kDa Na + /Ca 2+ exchanger is localized along the flagella of herring sperm (Vines et al, 2002).…”