Activación de espermatozoides de mamíferos con el ionóforo A23187

Mammalian spermatozoa acquire the fertilizing capacity in the female tract in a process called capacitation. However, only a very small fraction, estimated at around 10 per cent of the millions of spermatozoa that are produced and ejaculate, acquires this capacitation stage at a given time. Our hypothesis is that it is possible to activate other subpopulations not activated to acquire the ability to fertilize by inducing processes related to capacitation. At the molecular level, one of these processes is the increase in intracellular calcium. For this reason, Ca2plus ionophores, such as A23187, are commonly used as inducers of sperm capacitation by causing the entry of calcium into the cytoplasm of the spermatozoa and produce changes comparable to capacitation, such as the induction of a vigorous motility type known as hyperactivation. The aim of the present work was to achieve the activation of non-capacitated sperm subpopulations through the use of the Ca2plus ionophore A23187 (referred to hereafter as ionophore) in both mouse and bull. In mouse spermatozoa we observed that the treatment with concentrations of 5 and 10 μM of ionophore caused hyperactivation and induction of the acrosome reaction at the same level, reaching saturation in both responses. In addition, using a suboptimal concentration of spermatozoa to perform in vitro fertilization, treatment with 5 μM of ionophore increased the fertilization rate from 49 per cent obtained in the control to 68 per cent (P less than0.05 according to ANOVA). However, treatment with 10 μM caused a slight decrease in the fertilization rate with respect to the control indicating a certain level of toxicity at this concentration. In bull spermatozoa we observed a high level of acrosome reaction in the control sample (76 per cent). This was possibly due to the fact that we use cryopreserved samples and the freezing-thawing process could have induced the acrosome reaction by itself. The ionophore treatment did not increase this rate of acrosome reaction possibly because all the susceptible spermatozoa were already reacted by the freezing-thawing process itself. Nor did we find any effect of the ionophore treatment on the fertilizing capacity of these bull spermatozoa. The results indicate that in the mouse there is a subpopulation sensitive to activation by the ionophore that becomes hyperactive, loses its acrosome and is able to fertilize under in vitro conditions. However in bull we think that the process of sperm cryopreservation has already activated this subpopulation making it insensitive to the ionophore