We believe that the increase in sZP binding ability that takes place within the live spermatozoa is physiologically significant. We envisage that such increases in zona binding ability relate to optimal attachment of the sperm to the zona pellucida, thus improving chances for fertilization. The increased zona binding ability may also reflect sensitization of the sperm to induction of the acrosome reaction by zona components. Although noncapacitated spermatozoa can bind to the zona pellucida , incubation under IVF conditions has been shown to develop or increase the ability of sperm to undergo the zona-induced acrosome reaction and to fertilize in vitro. buy ortho tri-cyclen
The development of these latter abilities seems to depend on the same presence of Ca2+ (c.f. ) and bicarbonate that we found in the present study to be prerequisites for the increase of the capacity to bind zona proteins. Moreover, the time needed for the increase of the capacity to bind zona proteins is of the same order as the time needed for acquisition of the ability to penetrate the zona pellucida during pig IVF (e.g., ). Thus, the observed increase in the binding of zona proteins could well reflect changes that are necessary for effective sperm-zona interaction. It is noteworthy that the conditions optimal for pig IVF (i.e, incubation in the caffeine-supplemented bicarbonate-containing Tyrode’s medium TBC; see ) were also those that led to the most rapid development of enhanced zona binding ability as found in this study.