title: Roles of extracellular ions and pH in 5-HT-induced sperm motility in marine bivalve.
abstract: Factors that inhibit and stimulate the initiation of sperm motility were determined for Manila clam (Ruditapes philippinarum), Pacific oyster (Crassostrea gigas), and Japanese scallop (Patinopecten yessoensis). Compared with artificial seawater (ASW), serotonin (5-hydroxytryptamine creatinine sulfate, 5-HT) could fully trigger sperm motility and increase sperm velocity and motility duration. Sperm motility was decreased in ASW at pH 6.5-7.0 and suppressed at pH 4.0. In Manila clam and Pacific oyster, 5-HT could overcome the inhibitory effects of acidic pH on sperm motility. In the presence of nigericin (a K(+)/H(+) exchanger), sperm motility was only triggered at pH 8.3. Testicular fluid K(+) concentrations were two- to fourfold higher than that in ASW. Sperm motility and velocity were decreased in ASW or 5-HT containing ≥40  mM K(+) or ≥2.5  mM 4-aminopyridine, suggesting K(+) efflux requirement to initiate motility. Sperm motility and velocity were reduced in ASW or 5-HT containing EGTA or W-7, suggesting that extracellular Ca(2)(+) is required for Ca(2)(+)/calmodulin-dependent flagellar beating. Ca(2)(+) influx occurs via Ca(2)(+) channels because sperm motility and velocity were decreased in both ASW and 5-HT containing T-type and L-type Ca(2)(+) channel blockers. 5-HT-dependent initiation of sperm motility was associated with intracellular Ca(2)(+) rise, which was comparable to that seen in ASW but was not observed in the presence of EGTA or a Ca(2)(+) channel blocker. Extracellular Na(+) is also essential for sperm motility initiation via regulation of Na(+)/Ca(2)(+) exchange. Overall, 5-HT-dependent initiation of sperm motility in marine bivalve mollusks is an osmolality-independent mechanism and regulated by extracellular pH, K(+), Ca(2)(+), and Na(+).
authors.affiliation: Laboratory of Aquacultural Biology, Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-amamiyamachi, Sendai 981-8555, Japan.
authors.forename: Sayyed Mohammad Hadi
authors.initials: SM
authors.lastname: Alavi
authors.forename: Natsuki
authors.initials: N
authors.lastname: Matsumura
authors.forename: Kogiku
authors.initials: K
authors.lastname: Shiba
authors.forename: Naoki
authors.initials: N
authors.lastname: Itoh
authors.forename: Keisuke G
authors.initials: KG
authors.lastname: Takahashi
authors.forename: Kazuo
authors.initials: K
authors.lastname: Inaba
authors.forename: Makoto
authors.initials: M
authors.lastname: Osada
mesh_terms: D000818:Animals; D049872:Bivalvia; D002118:Calcium / Q000494:pharmacology; D003404:Creatinine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D005110:Extracellular Space; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000494:pharmacology*; D008297:Male; D011188:Potassium / Q000494:pharmacology; D012623:Seawater / Q000737:chemistry; D012701:Serotonin / Q000494:pharmacology*; D012964:Sodium / Q000494:pharmacology; D013081:Sperm Motility / Q000187:drug effects*
chemical_list: D004338:Drug Combinations; D007477:Ions; C014050:creatinine sulfate, serotonin drug combination; D012701:Serotonin; D012964:Sodium; D003404:Creatinine; D011188:Potassium; D002118:Calcium