CAMP ATP RELATIONSHIP IN THE ACTIVATION OF TROUT SPERM MOTILITY - THEIR INTERACTION IN MEMBRANE-DEPRIVED MODELS AND IN LIVE SPERMATOZOA/

Live trout spermatozoa initiate flagellar motility for only a short pe riod (30 sec at 18 degrees C) during which their mean beat frequency d ecreases steadily from 60 to 20 Hz. Motility then stops abruptly. Inve stigations of the activation of movement in demembranated sperm points to cyclic-AMP being necessary for reactivation (half effect at 0.5 mu M) in some conditions. cAMP acts mainly by increasing the percentage of motile cells and not the beat frequency (BF) of the flagellar axone me. Dibutyryl cAMP does not initiate movement or prolong motility of l ive sperm. The initiation of movement of demembranated trout sperm was investigated in various incubation conditions relative to previous ph ases of in vivo movement and to ATP concentration. In the absence of c AMP and in the presence of ATP lower than 25 mu M, all sperm cell mode ls were active with BF up to 15-20 Hz whatever their previous physiolo gical conditions. In contrast, at ATP concentrations above 100 mu M, t he fraction of active spermatozoa decreased proportionally but the BF of the active ones increased so that, at 1 mM ATP, only 5% were active but with a BF of 65 Hz: the addition of cAMP up to 20 mu M restored a ctivity to 100% sperm models with a similar BF of 65 Hz. At ATP concen trations higher than 25 mu M, cAMP was necessary in a concentration de pendent manner in the reactivation, but not in the demembranation medi um. This dependence was found to be unrelated to a previous in vivo ph ase of movement. The antagonistic effects of ATP vs. cAMP were tested at various concentrations of both nucleotides: the apparent affinity f or cAMP, measured as the concentration restoring movement of 50% cell models, was decreased from 15 nM at O.1 mM ATP to 0.5 mu M at 1 mM ATP ; conversely, the affinity for ATP, measured as the concentration givi ng rise to the half maximal beat frequency, was not significantly affe cted when the concentration of cAMP was raised to 0.5 mM. Preincubatio n with phosphodiesterase (PDE) resulted in motility of 100% of sperm m odels even at low ATP concentration. This tends to show that cAMP must be constantly present to sustain motility. Live spermatozoa showed a rise in cAMP which peaked after 100% of spermatozoa had initiated move ment. In some under- or over-mature sperm samples, the cAMP requiremen t for activation could be by-passed even at mM ATP concentrations. We suggest that the cAMP level could be one regulating factor responsible for the switch off mechanism occurring at 30 sec post-initiation and which identifies the end of the motility phase. (C) 1995 Wiley-Liss, I nc.