Impact of Ca2+ flux inhibitors on acrosome reaction of hamster spermatozoa.

ABSTRACT

Ca(2+) 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 Ca(2+) is essential, researchers have reported conflicting results as to what happens to Ca(2+) flux across the sperm membrane during capacitation and AR. The purpose of the present study was to further delineate the function of Ca(2+) 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 10(7) motile sperm/mL and incubated in 200-microL droplets for 4 hours at 37 degrees C in the presence of trifluoperazine (TFP), a calmodulin inhibitor, at 25, 50, 100, or 150 nM; verapamil (VP), a Ca(2+) channel inhibitor, at 25, 50, 100, or 150 nM; or nifedipine (NF), a voltage-dependent Ca(2+) 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 Ca(2+) 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 Ca(2+) channel inhibitors suppress sperm AR.