Tyrosine kinase-independent inhibition by genistein on spermatogenic T-type calcium channels attenuates mouse sperm motility and acrosome reaction

Although the protein tyrosine kinase (PTK) inhibitor, genistein, has been widely used to investigate the possible involvement of PTK during reproductive functions, it is unknown whether it modulates sperm calcium channel activity. In the present study, we recorded T-type calcium currents (ICa,T) in mouse spermatogenic cells using whole-cell patch clamp and found that extracellular application of genistein reversibly decreased ICa,T in a concentration-dependent manner (IC50 ∼22.7 μM). To determine whether TK activity is required for ICa,T inhibition, we found that peroxovanadate, a tyrosine phosphatase inhibitor, was ineffective in preventing the inhibitory effect of genistein. Furthermore, intracellular perfusion of the cells with ATP-γ-S also did not alter the inhibitory effect of genistein. To further reveal the direct inhibitory mechanism of genistein on ICa,T, we applied into the bath lavendustin A, a PTK inhibitor structurally unrelated to genistein, and found that the current amplitude remained unchanged. Moreover, daidzein, an inactive structural analog of genistein, robustly inhibited the currents. The inhibitory effect of genistein on T-type calcium channels was associated with a hyperpolarizing shift in the voltage-dependence of inactivation. Genistein was observed to decrease sperm motility and to significantly inhibit sperm acrosome reaction (AR) evoked by zona pellucida. Using transfected HEK293 cells system, only Cav3.1 and Cav3.2, instead of Cav3.3, channels were inhibited by genistein. Since T-type calcium channels are the key components in the male reproduction, such as in AR and sperm motility, our data suggest that this PTK-independent inhibition of genistein on ICa,T might be involved in its anti-reproductive effects.