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First published online November 17, 2005
Journal of Experimental Biology 208, 4549-4556 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01921
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K+-independent initiation of motility in chum salmon sperm treated with an organic alcohol, glycerol

M. Morita1,*, M. Fujinoki2 and M. Okuno1,{ddagger}

1 Department of Biology, Graduate School of Arts and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan
2 Department of Physiology, Dokkyo University School of Medicine, Mibu, Tochigi 321-0293, Japan

{ddagger} Author for correspondence (e-mail: cokuno{at}mail.ecc.u-tokyo.ac.jp)

Accepted 11 October 2005

Sperm of salmonid fishes are quiescent in the presence of millimolar concentrations of extracellular K+, but motility initiation occurs when sperm are suspended in K+-free medium. In this study, glycerol (CH2OHCHOHCH2OH) treatment of intact sperm in the presence of K+ induced the initiation of motility even though a large amount of K+ was present. Another organic alcohol, erythritol (CH2OH(CHOH)2CH2OH), had a similar effect, but ethylene glycol (CH2OHCH2OH) did not initiate sperm motility. Furthermore, this glycerol-treated sperm showed motility without subsequent addition of ATP and cAMP. CCCP, an uncoupler of the mitochondrial electron-transport chain involved in ATP synthesis, suppressed motility of glycerol-treated sperm, suggesting that ATP synthesis is required for dynein to slide microtubules in glycerol-treated sperm. The amount of intracellular cAMP ([cAMP]i) in glycerol-treated sperm did not increase on motility activation, but a protein kinase A (PKA) inhibitor, H-89, inhibited glycerol-treated sperm motility. In addition, phosphorylation of protein associated with motility initiation also occurred in glycerol-treated sperm, suggesting that the glycerol treatment induces activation of PKA without an increase in [cAMP]i. Taken together, it can be concluded that organic alcohol, glycerol and erythritol induce phosphorylation for motility initiation, bypassing the increase in [cAMP]i as a result of a decrease in extracellular K+ concentration.

Key words: sperm motility, salmon, organic alcohol, phosphorylation, cAMP, eukaryotic flagella


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