Figure 3. Phosphodiesterase (PDE) activity, intracellular levels of cyclic adenosine monophosphate (cAMP), and protein kinase A (PKA) activity in human spermatozoa during the acrosome reaction induced by calcium ionophore A23187. Spermatozoa were incubated for 3.5 hours in Biggers, Whitten, and Whittingham medium (BWW) alone (control) or supplemented with fetal cord serum ultrafiltrate (FCSu) and then treated for 15 minutes without (open bar) or with 1 µM A23187 (closed bar) as described in "Materials and Methods." PDE activity, reported as picomoles of cAMP per minute per 10⁸ spermatozoa (A), intracellular cAMP levels, reported as picomoles of cAMP per 10⁸ spermatozoa (B), and PKA activity, reported as picomoles of phosphate incorporated into Kemptide per minute per 10⁶ spermatozoa (C, D), were assayed. PKA activity was measured in the absence (C) or presence of dibutyryl-cAMP (dbcAMP) plus 3-isobutyl-1-methylxanthine (IBMX) (D). Values are mean plus or minus standard error of the mean of 4 independent experiments. ^* Value higher than that obtained with control spermatozoa. # Value higher than all others.