Adrenergic stimulation of sea urchin sperm cells

The noradrenergic agonists norepinephrine and isoproterenol elicit greater stimulatory swimming responses in sea urchin spermatozoa than epinephrine. The beta-blocker atenolol induces an even greater motile rate, while the alpha-blocker phentolamine has only a moderate effect, it also causes a minimal reduction in the sperm cells' response to atenolol. Caffeine increases the motility but to a lesser degree than 8-Br-cAMP. In drug interaction assays, both caffeine and 8-Br-cAMP depress the adrenergic effects. Agents that affect access of calcium to the flagellar apparatus (verapamil and trifluoperazine) depress the motility below the level of the controls when incubated separately with the sperm suspensions and counteract the stimulation due to atenolol. Adrenergic modulation of sperm motility thus appears to be both a calcium-dependent and a cyclic nucleotide-dependent process.