Adenine Nucleotides Modulate Mouse Sperm Flagellar Movement Patterns.

Abstract

Hyperactivation, a swimming pattern of mammalian sperm in the oviduct, is essential for fertilization. It is characterized by highly asymmetrical flagellar beating, which is triggered by a rise in flagellar cytoplasmic Ca2+. In vivo, hyperactivation may be modulated to direct sperm toward oocytes. In our previous work, by using mouse sperm which have hook-shaped heads, we demonstrated that the dominant bend of an asymmetrical beat can curve in the same direction as the curve of the hook in the head (pro-hook) or in the opposite direction (anti-hook). Dominant pro-hook and anti-hook flagellar beats are each triggered by rises in Ca2+, but the mechanisms by which Ca2+ can trigger one or the other remain poorly understood. ATP and ADP are also reported to affect flagellar bend amplitude; therefore, we hypothesized that adenine nucleotides interact with Ca2+ at the axoneme to regulate the asymmetry of the flagellar beat. To investigate the effect of ATP, ADP, and Ca2+, we applied ATP or ADP to demembranated mouse sperm model, with free Ca2+ buffered below 30 nM or at 600 nM. Briefly, sperm were demembranated in a 0.1% Triton-X-100 buffered solution and then reactivated in a solution providing an intracellular ionic environment. Ca2+ in the reactivation solution was buffered by 0.5 mM BAPTA. We found that reactivating with 4 mM ATP alone produced moderate pro-hook bending in 70-74% of reactivated sperm, whereas treatment with 4 mM ADP triggered a moderate anti-hook bending with a lower beating frequency (1.1 ± 0.2 beats/sec) in 85-88% reactivated sperm. Moreover, about 50-55% of sperm that were reactivated with ATP showed a stiff flagellar midpiece, whereas the entire flagellum was flexible when sperm were reactivated with ADP. In the presence of 600 nM free Ca2+, 85-90% reactivated sperm in the presence of either ATP or ADP showed deep anti-hook bends. AMP did not reactivate sperm in the absence of ATP or ADP. We concluded that the direction of the primary bend can be modulated by the amount of intracellular ATP and ADP available to the axoneme. NIH 1R03HD062471-01 and 5R01HD057144. (platform)