title: The physiological role of ADP and Mg2+ in maintaining a stable beat cycle in bull sperm.
abstract: Sperm flagella derive their motive power from the motor protein dynein. In this study, we show that maintenance of the flagellar beat cycle in detergent-extracted bull sperm models is highly dependent on the ratio of Mg(2+) to adenosine triphosphate (ATP). An excess of either ATP un-complexed with Mg(2+) , or an excess of Mg(2+) without an equivalent concentration of ATP, results in the loss of beat amplitude and a reduced curvature development in the beat cycle. In addition, we find that adenosine diphosphate (ADP) can stabilize the beat cycle and permit rhythmic beating across a broader range of ATP and Mg(2+) concentrations. We provide evidence that suggests that when ATP is un-complexed with Mg(2+) , it disrupts the beat cycle by reducing dynein adhesion and thereby, reduces the transmission of dynein-generated force between the doublets. Excess Mg(2+) does not act by the same mechanism and induces a condition where the flagellum is more resistant to bending. This is consistent with the idea that high Mg(2+) stabilizes rigor bridges, and ATP reduces the microtubule binding affinity of dynein. Our results may explain how intact sperm are able to sustain coordinated flagellar beating under a wide range of metabolic conditions, as intact sperm produce ADP in direct proportion to their consumption of ATP.
authors.affiliation: Department of Biological Sciences, Oakland University, Rochester, Michigan.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Lindemann
authors.forename: Tania G
authors.initials: TG
authors.lastname: dePinho
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Lesich
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D004398:Dyneins / Q000378:metabolism*; D005407:Flagella; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D013081:Sperm Motility; D013094:Spermatozoa / Q000502:physiology*
chemical_list: D000244:Adenosine Diphosphate; D004398:Dyneins; D008274:Magnesium
keywords: beat cycle; cilia; dynein; flagella; geometric clutch; motility; nucleotide regulation