title: Membrane hyperpolarization by sperm-activating and -attracting factor increases cAMP level and activates sperm motility in the ascidian Ciona intestinalis.
abstract: In the ascidian Ciona intestinalis (and C. savignyi), sperm-activating and -attracting factor (SAAF) is released from the egg at fertilization and stimulates both Ca(2+) influx and a transient increase in cAMP level of the sperm, leading to the activation of sperm motility (M. Yoshida et al., 1994, Dev. Growth Differ. 36, 589-595). In this paper we show in C. intestinalis that valinomycin, a potassium-selective ionophore, as well as SAAF, activated sperm motility, and this activation was suppressed by extracellular high K(+). Membrane potential measurements showed that both SAAF and valinomycin increase K(+) permeability of sperm and induce membrane hyperpolarization, the amplitude of which depends on the external K(+) concentration. The membrane potential and intracellular K(+) concentration of Ciona sperm without SAAF were estimated to be about -50 mV and 560 +/- 40 mM, respectively. After treatment with SAAF or valinomycin the membrane potential became almost equal to the equilibrium potential of K(+) (-100 mV), and the cAMP level increased in artificial seawater. A potent voltage-dependent K(+) channel blocker, MCD peptide, at the concentration of 10 microM blocked SAAF-induced hyperpolarization of the cells, increase in cAMP, and sperm motility. These results suggest that membrane hyperpolarization produced by the opening of K(+) channels elevates cAMP synthesis and leads to the activation of sperm motility in Ciona.
authors.affiliation: Misaki Marine Biological Station, University of Tokyo, Misaki, Miura, Kanagawa, 238-0225, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Izumi
authors.forename: T
authors.initials: T
authors.lastname: Márián
authors.forename: K
authors.initials: K
authors.lastname: Inaba
authors.forename: Y
authors.initials: Y
authors.lastname: Oka
authors.forename: M
authors.initials: M
authors.lastname: Morisawa
mesh_terms: D000818:Animals; D002938:Ciona intestinalis / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D004527:Egg Proteins / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials; D011188:Potassium / Q000502:physiology; D015221:Potassium Channels / Q000502:physiology; D013081:Sperm Motility / Q000187:drug effects* / Q000502:physiology*
chemical_list: D004527:Egg Proteins; D007476:Ionophores; D015221:Potassium Channels; D000242:Cyclic AMP; D011188:Potassium