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Impact of Ca²⁺ Flux Inhibitors on Acrosome Reaction of Hamster Spermatozoa

YI B. HAN

LEI J. ZHENG

From the ^* Center for Human Reproduction, North Shore University Hospital, New York University School of Medicine, Manhasset, New York; Department of Obstetrics and Gynecology, Chinese University of Hong Kong, Hong Kong, China; and Columbia University Center for Women's Reproductive Care, New York, New York.

Correspondence to: Dr Huai L. Feng, Associate Professor, The Center for Human Reproduction, Department of Obstetrics and Gynecology, North Shore University Hospital, 300 Community Dr, Manhasset, NY 11030 (e-mail: hfeng{at}nshs.edu).

Ca²⁺ plays a prominent role in the regulation of critical functions of spermatozoa, such as capacitation, acrosome reaction (AR), and fertilization. While there is consensus that Ca²⁺ is essential, researchers have reported conflicting results as to what happens to Ca²⁺ flux across the sperm membrane during capacitation and AR. The purpose of the present study was to further delineate the function of Ca²⁺ channels and their role in sperm capacitation and AR. Epididymides were obtained from healthy adult male hamsters. Spermatozoa were washed with modified Tyrode medium supplemented with 0.3% bovine serum albumin, adjusted to 4.5 x 10⁷ motile sperm/mL and incubated in 200-µL droplets for 4 hours at 37°C in the presence of trifluoperazine (TFP), a calmodulin inhibitor, at 25, 50, 100, or 150 nM; verapamil (VP), a Ca²⁺ channel inhibitor, at 25, 50, 100, or 150 nM; or nifedipine (NF), a voltage-dependent Ca²⁺ channel inhibitor, at 50, 100, 200, or 400 nM. Spermatozoa were assessed for AR by using Coomassie brilliant blue staining techniques. Results indicated that incubation of sperm with Ca²⁺ channel inhibitors for 4 hours significantly reduced AR in the study groups (TFP: 88% ± 2.3%, 65% ± 2.0%, 60% ± 2.2%, 54 % ± 2.2%, respectively; VP: 45% ± 1.3%, 23 % ± 1.2%, 12% ± 1.0%, 8% ± 0.6%, respectively; and NF: 11% ± 0.8%, 9% ± 0.3%, 7.0% ± 0.1%, 6.0% ± 0.1%, respectively) compared with control group (95% ± 3.0%, P < .05). However, increasing the concentrations of TFP and NF did not result in further suppression of AR. In summary, the antagonists of calmodulin and Ca²⁺ channel inhibitors suppress sperm AR.

     Key words: Calcium

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