AJA publishes new findings in basic and clinical (including modern, traditional and epidemiological) research on Andrology.

Mammalian sperm acquire fertilizing ability in the female tract in a process known as capacitation. At the molecular level, capacitation is associated with up‐regulation of a cAMP‐dependent pathway, changes in intracellular pH, intracellular Ca²⁺, and an increase in tyrosine phosphorylation. How these signaling systems interact during capacitation is not well understood. Results presented in this study indicate that Ca²⁺ ions have a biphasic role in the regulation of cAMP‐dependent signaling. Media without added Ca²⁺ salts (nominal zero Ca²⁺) still contain micromolar concentrations of this ion. Sperm incubated in this medium did not undergo PKA activation or the increase in tyrosine phosphorylation suggesting that these phosphorylation pathways require Ca²⁺. However, chelation of the extracellular Ca²⁺ traces by EGTA induced both cAMP‐dependent phosphorylation and the increase in tyrosine phosphorylation. The EGTA effect in nominal zero Ca²⁺ media was mimicked by two calmodulin antagonists, W7 and calmidazolium, and by the calcineurin inhibitor cyclosporine A. These results suggest that Ca²⁺ ions regulate sperm cAMP and tyrosine phosphorylation pathways in a biphasic manner and that some of its effects are mediated by calmodulin. Interestingly, contrary to wild‐type mouse sperm, sperm from CatSper1 KO mice underwent PKA activation and an increase in tyrosine phosphorylation upon incubation in nominal zero Ca²⁺ media. Therefore, sperm lacking Catsper Ca²⁺ channels behave as wild‐type sperm incubated in the presence of EGTA. This latter result suggests that Catsper transports the Ca²⁺ involved in the regulation of cAMP‐dependent and tyrosine phosphorylation pathways required for sperm capacitation. J. Cell. Physiol. 230: 1758–1769, 2015.

Signaling events leading to mammalian sperm capacitation rely on activation/deactivation of proteins by phosphorylation. This cascade includes soluble adenylyl cyclase, an atypical bicarbonate-stimulated adenylyl cyclase, and is mediated by protein kinase A and the subsequent stimulation of protein tyrosine phosphorylation. Recently, it has been proposed that the capacitation-associated increase in tyrosine phosphorylation is governed by Src tyrosine kinase activity. This conclusion was based mostly on the observation that Src is present in sperm and that the Src kinase family inhibitor SU6656 blocked the capacitation-associated increase in tyrosine phosphorylation. Results in the present manuscript confirmed these observations and provided evidence that these inhibitors were also able to inhibit protein kinase A phosphorylation, sperm motility, and in vitro fertilization. However, the block of capacitation-associated parameters was overcome when sperm were incubated in the presence of Ser/Thr phosphatase inhibitors such as okadaic acid and calyculin-A at concentrations reported to affect only PP2A. Altogether, these data indicate that Src is not directly involved in the observed increase in tyrosine phosphorylation. More importantly, this work presents strong evidence that capacitation is regulated by two parallel pathways. One of them requiring activation of protein kinase A and the second one involving inactivation of Ser/Thr phosphatases.