What does a Common Channel for Electrolytes and Non-electrolytes in the Sperm Mean?

Osmotic Tolerance of Equine Spermatozoa and the Effects of Soluble Cryoprotectants on Equine Sperm Motility, Viability, and Mitochondrial Membrane Potential

“…In addition to the active movement of ionic constituents, there is increasing evidence that spermatozoa may possess selective water channels that facilitate movement of water across the sperm membrane at a greater rate than can be accounted for by diffusion alone. Spermatozoa generally have a very high water permeability (Noiles et al, 1993;Liu et al, 1995) that appears to be mediated by the presence of water channels (Curry et al, 1995;Ishibashi et al, 1997;Sitaramam and Sauna 2000). Evidence for the nature of these water channels (aquaporins) in spermatozoa has been lacking ; however, an aquaporin has recently been identified in rat testis and spermatozoa, and appears to serve as a channel that allows permeation of both water and glycerol (Ishibashi et al, 1997).…”

“…Evidence for the nature of these water channels (aquaporins) in spermatozoa has been lacking ; however, an aquaporin has recently been identified in rat testis and spermatozoa, and appears to serve as a channel that allows permeation of both water and glycerol (Ishibashi et al, 1997). Although the functional significance of a high water permeability through specific channels in spermatozoa has not been well defined, there is a suggestion on an evolutionary basis that such mechanisms may be important in the function of spermatozoa from aquatic species with external fertilization (Sitaramam and Sauna, 2000). Whatever the evolutionary basis for these water channels, the high water permeability of spermatozoa directly effects their sensitivity to osmotic stress induced during the addition and removal of permeable solutes such as glycerol.…”