Recently, Dobrinski and coworkers demonstrated that the intracellular calcium concentration ([Ca2+]j) of equine sperm attached to oviductal epithelial cells was maintained at levels 2- to 3-fold lower than in free-swimming sperm. However, it was not clear from this study whether sperm cells with lower [Ca2+]; preferentially bound to oviductal epithelial cells or whether [Ca2+]; remained low as a result of binding. When equine sperm were incubated with oAMV from preovulatory isthmic epithelial cells, a situation akin to being continuously attached to oviductal epithelial cells but still free to swim unimpeded, [Ca2+]; was maintained at low levels in all sperm. This observation supports the notion that direct contact with the apical plasma membrane of oviductal epithelial cells results in the maintenance of low intracellular calcium. Furthermore, maintenance of low [Ca2+]j was not observed in the presence of Fab that reduce oAMV binding to sperm, suggesting that a specific molecular interaction between sperm and oAMV was responsible for maintaining low [Ca2+]j (Fig. 4). buy levaquin online
In sum, the available evidence suggests the following: on route to the site of fertilization, sperm temporarily adhere to the apical plasma membrane of the epithelial cells that line the oviductal isthmus. During the period of adherence, sperm viability is maintained and capacitation proceeds at a slower rate. This prolongs the fertilizable life span of the sperm and maximizes the probability of conception when ejaculation is not coincident with ovulation. These effects on viability and capacitation are likely to be mediated, at least in part, through the maintenance of low intracellular calcium within the sperm. Although much has yet to be determined regarding the molecular mechanisms underlying such effects, direct oviductal epithelial-sperm interactions clearly play an important role in the success of the reproductive process.
FIG. 4. Intracellular calcium concentration ([Ca2+];) in equine spermatozoa incubated with either isthmic oAMV, antibody fragments (Fab) raised against equine periacrosomal sperm plasma membrane, or oAMV and Fab combined. Medium for culture was Tyrode’s albumin lactate pyruvate medium (TALP). Least-squares means ± SEM, n = 6 ejaculates. Data were analyzed by ANOVA for the effects of time, treatment, and interactions. Pair-wise comparisons of means were made using Tukey’s studentized range test (HSD). Means with different letters are significantly different (p < 0.05). Adapted from Dobrinski et al., Biol Reprod 1997; 56:866, Figure 6.