title: Regulation of axonemal motility in demembranated equine sperm.
abstract: Equine in vitro fertilization is not yet successful because equine sperm do not effectively capacitate in vitro. Results of previous studies suggest that this may be due to failure of induction of hyperactivated motility in equine sperm under standard capacitating conditions. To evaluate factors directly affecting axonemal motility in equine sperm, we developed a demembranated sperm model and analyzed motility parameters in this model under different conditions using computer-assisted sperm analysis. Treatment of ejaculated equine sperm with 0.02% Triton X-100 for 30 sec maximized both permeabilization and total motility after reactivation. The presence of ATP was required for motility of demembranated sperm after reactivation, but cAMP was not. The calculated intracellular pH of intact equine sperm was 7.14 ± 0.07. Demembranated sperm showed maximal total motility at pH 7. Neither increasing pH nor increasing calcium levels, nor any interaction of the two, induced hyperactivated motility in demembranated equine sperm. Motility of demembranated sperm was maintained at free calcium concentrations as low as 27 pM, and calcium arrested sperm motility at much lower concentrations than those reported in other species. Calcium arrest of sperm motility was not accompanied by flagellar curvature, suggesting a failure of calcium to induce the tonic bend seen in other species and thought to support hyperactivated motility. This indicated an absence, or difference in calcium sensitivity, of the related asymmetric doublet-sliding proteins. These studies show a difference in response to calcium of the equine sperm axoneme to that reported in other species that may be related to the failure of equine sperm to penetrate oocytes in vitro under standard capacitating conditions. Further work is needed to determine the factors that stimulate hyperactivated motility at the axonemal level in equine sperm.
authors.affiliation: Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas.
authors.forename: Shavahn C
authors.initials: SC
authors.lastname: Loux
authors.affiliation: Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas.
authors.forename: Beatríz
authors.initials: B
authors.lastname: Macías-Garcia
authors.affiliation: Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas.
authors.forename: Lauro
authors.initials: L
authors.lastname: González-Fernández
authors.affiliation: Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas.
authors.forename: Heloisa DeSiqueira
authors.initials: HD
authors.lastname: Canesin
authors.affiliation: Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas.
authors.forename: Dickson D
authors.initials: DD
authors.lastname: Varner
authors.affiliation: Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas Department of Large Animal Clinical Sciences, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University, College Station, Texas khinrichs@cvm.tamu.edu.
authors.forename: Katrin
authors.initials: K
authors.lastname: Hinrichs
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D054468:Axoneme / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology; D002458:Cell Fractionation; D002462:Cell Membrane; D000242:Cyclic AMP / Q000494:pharmacology; D006736:Horses / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D008297:Male; D009038:Motion; D013081:Sperm Motility / Q000502:physiology; D013094:Spermatozoa / Q000166:cytology / Q000648:ultrastructure
chemical_list: D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D002118:Calcium
keywords: calcium; demembranated; equine; hyperactivated motility; pH; sperm; stallion