Involvement of thapsigargin-sensitive Ca²⁺-ATPase in the occurrence of helical movement with 3-D rotation in cryopreserved bovine sperm

抄録

We previously reported that reduction of cAMP signaling activity converts the motility patterns from planar [P] movement to helical [H] movement with 3-D rotation in non-cryopreserved bovine sperm. Although similar changes were observed after cryopreservation, inducers of H movement have not been identified in cryopreserved sperm yet. In this study, we have reported the motility patterns in cryopreserved sperm treated with NaHCO₃ to stimulate cAMP signaling activity and non-cryopreserved sperm treated with thapsigargin to reduce Ca²⁺-ATPase activity. In cryopreserved sperm, H movement (about 50% on average) was predominant over P movement (about 25%). These proportions were scarcely affected by adding NaHCO₃. In contrast, in non-cryopreserved sperm, H movement (about 25%) was lesser than P movement (about 50%). After washing, the average percentage of sperm exhibiting H movement was about 25% and then significantly increased to around 50% by incubation with thapsigargin in the presence of CaCl₂. Moreover, the immunodetection indicated that 140-kDa thapsigargin-sensitive Ca²⁺-ATPases were localized in the sperm neck. Additionally, percentages of cryopreserved sperm exhibiting H movement showed inter-individual differences and a significant correlation with the results of artificial insemination (r=0.8061), indicating the importance of H movement in sperm fertilizing ability. Considering the previous report that cryopreservation increased the intracellular Ca²⁺ level probably by reducing Ca²⁺- ATPase activity, these results suggest that the reduction of thapsigargin-sensitive Ca²⁺-ATPase activity in the neck promotes H movement with 3-D rotation in cryopreserved bovine sperm.