Survival of drowning sperm: Do spermatozoa from external fertilizers adapt to differing osmotic environments through the use of aquaporins?

摘要

In spawning animals, external fertilization usually requires spermatozoa to become activated (motile) in the environmental medium and then quickly locate and contact the egg. In most teleost fish, sperm are usually quiescent within the testes and seminal fluid but then initiate vigorous motility upon dilution into the external medium in which spawning occurs [1]. In teleost fish sperm, an increase in intracellular calcium occurs upon motility initiation by way of different signaling mechanisms (reviewed by [2]) [3-5]. Following dilution into medium, four different triggers of sperm motility in teleosts have been identified: 1) a reduction in external K~+ upon dilution of semen initiates motility in salmonids [6, 7], 2) hypotonic exposure after dilution into freshwater is the trigger in nonsalmonid freshwater fishes [8-11], 3) hypertonic exposure initiates sperm motility in marine teleosts [12, 13], and 4) egg-associated molecules activate sperm motility [14-171.