AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 5 1363-R1370, Copyright © 1994 by American Physiological Society
Hyperosmolality and sperm storage in hibernating bats: prolongation of sperm life by dehydration
E. G. Crichton, B. T. Hinton, T. L. Pallone and R. H. Hammerstedt
Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park 16802.
Osmolalities of epididymal fluids obtained by micropuncture from
hibernating species of bats (Myotis lucifugus) rise during sperm storage
periods to as high as 1,523 mmol/kgH2O (approximately 5 times that of
plasma). In vitro studies establish that hyperosmolality can preserve
viability and prevent initiation of progressive motility in bat epididymal
spermatozoa as well as induce their quiescence by reducing respiration.
Reduction of osmolality (to 500-600 mmol/kgH2O) induces swelling of sperm
and allows the initiation of motility and increased metabolic rate; further
reduction of osmolality to < 300 mmol/kgH2O compromises permeability
barriers and causes loss of motility. We hypothesize that seasonal
establishment of hyperosmotic conditions driven by those cells that
constitute the limits of the epididymal lumen dehydrates the compliant
spermatozoa and thereby minimizes their metabolic needs. A novel form of
cell storage dependent on unique adaptations of the epididymal epithelium
for solute and water transport is implicated. To date, the operative
osmolyte or osmolytes responsible for elevating osmolality in this system
remain elusive.
