Urocortin(UCN),a newly isolated peptide,has been found to play an important role mainly in female reproductive system.In order to investigate the effect of UCN on T-type calcium currents(ICa,T), exploring the mechanisms of UCN s role in male reproductive system,especially in acrosome reaction,we directly measured the ICa,T in mouse spermatogenic cells exposed to UCN using standard whole-cell patch clamp recording technique.Our results showed that UCN reversibly inhibited the T-type Ca2+ currents in the cells in a concentration-dependent manner.The current density was inhibited by about 19% after exposure of the cells to UCN(0.1 lM)for 5 min,from the control value of 6.75±1.17 to 5.26±0.82 pA/pF.UCN up-shifted the current-voltage(I-V)curve.Frequency-dependence of UCN’s effects on ICa,T was also observed.Moreover,UCN at 0.1 lM did not markedly affect the activation of ICa,T but shifted the inactivation curve of ICa,T to the left.The inhibitory effect of UCN on the T-type Ca2+ current was not affected by Astressin,the CRF receptor blocker.Since T-type calcium channels are a key component in acrosome reaction,our data suggest that UCN might be a significant factor in male reproductive action and a potential contraceptive agent.