Electrophoretic properties of bull and of rabbit spermatozoa

Abstract

The electrophoretic properties of live, potentially fertile spermatozoa were investigated over a wide range of pH at constant ionic strength. As electrophoretic mobility measurements could be performed only on immotile cells, the motile spermatozoa were inactivated temporarily, either by low temperature or by CO 2 at room temperature. In both cases motility could be fully restored and the surface charge was unaffected by the method of inactivation. Reversible inactivation of the spermatozoa could be achieved by the electric field as well, but only at high current densities which cause convection currents in the liquid due to heating that obscure the electrophoretic migration. A current density of 0.3 ampere/cm 2 at a field strength of 21.5 volt/cm will inactivate the cells after 40–50 sec. Electrophoretic mobility measurements at low temperatures were performed in a specially designed thermostated microelectrophoresis apparatus, whose construction and operation are described. The sperm were found to he electrophoretically homogeneous, with a normal distribution of mobilities over a rather narrow range. Mean mobility determinations were reproducible within ± 2 per cent. The electrophoretic mobilities of originally immotile and of inactivated spermatozoa from the same sample were the same. The electrophoretic mobilities of spermatozoa in seminal plasma alone, in the presence of egg-yolk, and after washing, were the same. The isoelectric point of the sperm surface was found to be 3.4 ± 0.05. No positively charged and negatively charged spermatozoa were found in the same suspension at any one pH, between pH 2.5 and 8.5, in a variety of buffers, in either bull or rabbit sperm. Above the isoelectric point, passive electrophoretic migration was toward the anode with the tail extended forward. Below the isoelectric point they migrated toward the cathode with the head in the lead, i.e. maintaining the same head-tail orientation with respect to the electric field. Both head and tail were shown to have a net negative charge, above the isoelectric point, with the tail having the higher charge density. The mobilities of the separated heads and tails were determined and, as expected, the tail was found to have a higher mobility than the head with the mobility of the whole sperm intermediate between the two. The majority of motile spermatozoa were observed to exhibit galvanotactic migration toward the cathode—in the opposite direction to the electrophoretic migration. The possibility of sex control of offsprings by fractionation of the sperm on the basis of electrophoresis or galvanotaxis was discussed.