The motility recovery suggests that completion of axonemal maturation occurred during exposure to a hypertonic environment. In addition, upon dilution of sperm into a hypertonic glycerol solution prior to demembranation, the motility of demembranated sperm was reactivated in the absence of cAMP. Monitoring intracellular Ca 2+, using fluo-4, revealed that intracellular Ca 2+ increased when sperm were suspended in hypertonic solutions, and a subsequent dilution into a hypotonic solution led to a decrease in intracellular Ca 2+ concomitant with motility initiation. Elimination of intracellular Ca 2+ by BAPTA-AM significantly inhibited glycerol-treated sperm motility, whereas removal of extracellular Ca 2+ by EGTA did not. We found that treatment with solutions consisting of organic or inorganic ions, as well as glycerol, induced sperm motility in an osmolarity-dependent manner. In the present study, we further investigated the glycerol-induced motility mechanism.
In a previous study, however, we demonstrated that suspending sperm in a 10% glycerol solution and subsequent dilution into a low-osmotic solution induced motility independently of extracellular K + and cAMP. Salmonid fish sperm motility is known to be suppressed in millimolar concentrations of extracellular K +, and dilution of K + upon spawning triggers cAMP-dependent signaling for motility initiation.
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