Production of nitric oxide by sperm of the steelhead ( Oncorhynchus mykiss) and its actions on motility and respiration

Abstract

The objective was to characterize nitric oxide (NO) involvement in steelhead sperm physiology with respect to modulation of motility and quiescent sperm respiration, and to assess NO production. Activation of sperm motility in the presence of a NO scavenger (PTIO) decreased path straightness (STR; from 62 to 44%, P < 0.05) and wobble (indicator of lateral head movement, WOB; from 68 to 61%, P < 0.05), whereas activating solution containing a NO donor (SNAP) increased STR (from 62 to 71%, P < 0.05). Neither SNAP nor PTIO impacted percent motility or velocity when present in activating media alone. Incubation of quiescent sperm with SNAP reduced motility (from 96 to 53%, P < 0.0001), curvilinear velocity (from 156 to 83 μm/s P < 0.0001), and WOB (from 77 to 50%, P < 0.0001); however, these effects were abolished by inclusion of PTIO. Response of quiescent sperm to SNAP was reversible with time, whereas PTIO alone had no effect. Incubation of sperm with SNAP decreased respiration to approximately one half of control (P < 0.05). With the fluorescent NO indicator, DAF-FM DA, intracellular NO was detected in quiescent, but not activated, sperm. Incubation of activated sperm in an immobilization buffer resulted in reappearance of NO. In addition to illustrating NO sensitivity of steelhead sperm motility, we inferred that the effects of NO on quiescent sperm occurred via inhibition of respiration, and that these sperm produced NO prior to activation.