Sperm-immobilizing antibodies suppress an increase in the plasma membrane fluidity of human spermatozoa

Abstract

To clarify the mechanism by which capacitation is blocked by sperm-immobilizing antibodies, changes in the plasma membrane fluidity of human spermatozoa exposed to sperm-immobilizing antibodies were evaluated. In vitro cell culture study using human spermatozoa. Department of Obstetrics and Gynecology, School of Medicine, The University of Tokushima. Semen samples were obtained from four healthy, fertile volunteers. The internalization of [3H]lyso-platelet activating factor (lyso-PAF) across the plasma membranes of human spermatozoa, which were exposed to sperm-immobilizing antibodies (antisperm group) or not exposed (control group), was measured at 20 and 60 minutes after the addition of a phospholipid probe using the modified albumin-back extraction method. The percentage of internalization of [3H]lyso-PAF across the plasma membrane of human spermatozoa. Although the percentages of internalization of [3H]lyso-PAF (mean +/- SE) in the antisperm and control groups 20 minutes after addition of [3H]lyso-PAF were not significantly different (6.6% +/- 1.5% and 9.2% +/- 2.1%, respectively), at 60 minutes after the addition, the percentage in the antisperm group (9.0% +/- 1.3%) was significantly lower than that in the control group (13.4% +/- 1.3%). This inhibitory effect was diminished when spermatozoa exposed to sperm-immobilizing antibodies were incubated in an antibody-free medium. Sperm-immobilizing antibodies suppress the increase in internalization of an alkyl ester lysophospholipid probe in plasma membranes of human spermatozoa, and this inhibitory effect is reversible. Therefore, sperm-immobilizing antibodies suppress the fluidity of the plasma membranes of human spermatozoa, thus blocking capacitation.