Control of respiration and of motility in ejaculated bull spermatozoa

The relations between motility and respiration were studied in ejaculated bull spermatozoa respiring with lactate. Motility was quantitatively evaluated by a turbidimetric procedure as percentage of cells moving per minute from the bottom of the cuvette into the light path. For selective inhibition of ATP-consuming reactions including motility or of mitochondrial respiration, vanadate or cyanide, respectively, were used. Both inhibitors were found to produce proportional changes in motility and respiration. The simultaneous changes in motility and respiration were linked to shifts in the cellular ATP/ADP ratio. Partial uncoupling of respiration in vanadate-inhibited cells gave similar relations between respiration and ATP/ADP ratios as stepwise inhibition of ATP-utilizing reactions by vanadate. Presuming saturation kinetics with respect to the ATP/ADP ratio, half maximum constants of 1.7 and 4.7 for the ATP/ADP ratio and maximum values of about 130% and 300% (in comparison to untreated cells) were estimated for motility and respiration, respectively. Respiration showed a much steeper dependence on the ATP/ADP ratio than motility resulting in an apparent cooperativity coefficient of 2.9. From these dependences on the ATP/ADP ratio, the shares in the control of ATP turnover in untreated cells were estimated. At sufficient supply with substrate, more than 80% of control were excreted by motility and other ATP-utilizing reactions, the rest by mitochondrial ATP production, i.e., the reactions of oxidative phosphorylation.