Membrane Contact with Oviductal Epithelium Modulates the Intracellular Calcium Concentration of Equine Spermatozoa in Vitro1

Abstract

Interaction of equine spermatozoa with oviductal epithelial cells (OEC) prolongs sperm viability and maintains low intracellular calcium concentration ([Ca2+]i) in spermatozoa. Experiments were designed to investigate 1) whether release of spermatozoa from OEC in vitro is associated with elevated [Ca2+]i and 2) whether soluble products from OEC or direct membrane contact between spermatozoa and OEC mediates the effects of OEC on sperm [Ca2+]i. In the first experiment, changes in [Ca2+]i in spermatozoa loaded with indo-1 acetoxymethylester were determined in motile spermatozoa released from OEC monolayers after 4 h of culture compared to [Ca2+]i in spermatozoa still attached to OEC. In addition, [Ca2+]i was determined in spermatozoa incubated with OEC-conditioned medium for 6 h compared to that in spermatozoa incubated in control medium. [Ca2+]i was higher in motile spermatozoa released from OEC than in spermatozoa still attached to OEC after 4 h of incubation. Incubation in OEC-conditioned medium resulted in lower sperm [Ca2+]i only at 4 h of incubation, but not at 0.5, 2, or 6 h of incubation. In the second experiment, a suspension of apical plasma membrane vesicles (AMV) isolated from isthmic oviductal epithelium was used to study the specific effect of sperm contact with OEC membranes on sperm viability, capacitation, and [Ca2+]i. Direct membrane contact between spermatozoa and AMV prolonged sperm viability, delayed capacitation, and maintained low [Ca2+]i in spermatozoa. These results indicated that membrane contact between equine spermatozoa and OEC is required to maintain low [Ca2+]i, delay capacitation, and prolong viability of spermatozoa in vitro. Modulation of capacitation rate for spermatozoa stored in the isthmic sperm reservoir might ensure the availability of a competent sperm population at the time of fertilization.

Membrane transfer from oocyte to sperm occurs in two CD9-independent ways that do not supply the fertilising ability of Cd9-deleted oocytes

“…Similarly, human and equine sperm incubated with endosalpingeal membrane vesicles capacitate more slowly than sperm incubated in capacitating medium alone (Dobrinski et al 1997, Murray & Smith 1997.…”

“…CD9-independent membrane fragment transfer from the apical membranes of the endosalpinx (Dobrinski et al 1997, Murray & Smith 1997, Gwathmey et al 2006. Similarly, human and equine sperm incubated with endosalpingeal membrane vesicles capacitate more slowly than sperm incubated in capacitating medium alone (Dobrinski et al 1997, Murray & Smith 1997.…”

Sperm release from oviduct epithelial binding is controlled hormonally by peri‐ovulatory graafian follicles

“…In other words, bound spermatozoa may contribute to their own release from binding when they have achieved a suitable stage of maturity. In vitro studies of sperm-epithelial contact indicate that binding of spermatozoa can modulate the intracellular calcium concentration (Dobrinski et al, 1997) and alter the spectrum of proteins secreted by oviduct epithelial cells (Ellington et al, 1993;Thomas et al, 1995); the same appears true in vivo (Fazeli et al, 2004). If the modified proteins include binding proteins, then this would indeed suggest a component of self-regulation during the phase of release.…”

Kinetic characterization of the changes in protein tyrosine phosphorylation of membranes, cytosolic Ca2+ concentration and viability in boar sperm populations selected by binding to oviductal epithelial cells

“…However, the regulative role of the oviduct in vivo is not only to delay but also to promote capacitation to provide a sufficiently large population of cells capable of fertilization at the time of ovulation. In a number of studies performed in vitro and in vivo it has been demonstrated that capacitation and increase of cytosolic Ca 2+ concentration are involved in the release of spermatozoa from the epithelium (Smith and Yanagimachi, 1991;Lefebvre and Suarez, 1996;Dobrinski et al, 1997), and that sperm capacitation proceeds at a faster rate when mating occurs after ovulation (Smith and Yanagimachi, 1989). Therefore, it can be expected that the interaction of the oviduct with spermatozoa occurs in three main modes: selection, maintenance of 'low capacitation' state within a certain time window and promotion of capacitation (Fig.…”

“…Thus, the maintenance of viability and the modulation of capacitation by the oviduct, demonstrated in a number of studies using different animal models, are mutually associated events (Smith, 1998). In horses, [Ca 2+ ] i of spermatozoa attached to oviductal epithelial cells is maintained at lower concentrations than in free-swimming spermatozoa and direct contact with the apical plasma membrane of the epithelial cells seems to be responsible for the maintenance of low [Ca 2+ ] i (Dobrinski et al, 1996(Dobrinski et al, , 1997. These observations indicate that the regulation of Ca 2+ uptake in spermatozoa is an important feature of oviductal sperm reservoir function.…”