The male antifertility effect of a water-chloroform extract (GTW) from the root xylem of Tripterygium wilfordii has attracted worldwide interest. In the present study, by using whole-cell recording, the effects of GTW and two isolated monomers from GTW, demethylzeylasteral and L-epicatechin, on the T-type Ca(2+) channels in mouse spermatogenic cells were investigated. The results showed that each of them concentration-dependently and partially reversibly inhibited T-type Ca(2+) current in the cells. The IC(50) of GTW and demethylzeylasteral were approximate, while L-epicatechin inhibited the channels at a much higher concentration. The voltage dependence of the inhibitory effect and the changes in activation and inactivation time constants after application of these compounds were also examined. These data suggest that the inhibition of T-type Ca(2+) currents could be responsible for the antifertility activity of these compounds.