In the present investigation, we hypothesized that 1) the OEC should not bind capacitated sperm—otherwisesperm transport within the oviduct would be blocked; and 2) once sperm are bound to OEC, they are likely to become capacitated before release. Therefore, 3) it follows that the sperm-OEC interaction must be specific, causing alterations of sperm functional status not achieved by other cell types in vitro. To test these hypotheses, we used CTC to study the capacitation status of boar spermatozoa in coculture with homologous OEC and cells of nonreproductive origin (LLC-PK1, porcine kidney epithelial cell line). In addition, the preferential binding of uncapacitated, capacitated, or ac-rosome-reacted boar spermatozoa to OEC and the other cell type was also investigated. Our approach was to vary the proportions of uncapacitated, capacitated, or acrosome-re-acted boar spermatozoa in suspension using long preincubation and lysophosphatidylcholine (LPC) treatment of semen prior to a very short incubation with oviductal epithelial and LLC-PK1 cells.
We predicted that if uncapacitated boar spermatozoa preferentially bind to epithelial cells, then the majority of the spermatozoa bound to the epithelial cells should be uncapacitated and no relationship should exist between the proportion of uncapacitated boar spermatozoa in suspension and of those bound to epithelial cells. Conversely, such a relationship would be observed if sperm binding to epithelial cells were nonselective.
In a previous study we demonstrated the feasibility of using OEC obtained from prepubertal gilts in examining the sperm-oviduct interaction. Use of these cells in in vitro studies provides a constant and homogenous source of experimental material with a limited variation due to the age and cycle status of the donor. We used these cells in the current investigation to test further their capacity to interact with boar spermatozoa.