Participation of inositol trisphosphate and ryanodine receptors inBufo arenarumoocyte activation

Abstract

Calcium is considered the most important second messenger at fertilization. Transient release from intracellular stores is modulated through both agonist-gated channels, IP₃Rs and RyRs, which can be found individually or together depending on the oocyte species. Using the four commonly used compounds (thimerosal, caffeine, heparin and ruthenium red), we investigated the existence and interdependence of both IP₃Rs and RyRs in mature Bufo arenarum oocytes. We found that caffeine, a well known specific RyRs agonist, was able to trigger oocyte activation in a dose-dependent manner. Microinjection of 10 mM caffeine showed 100% of oocytes exhibiting characteristic morphological criteria of egg activation. Ruthenium red, the specific RyR blocker, was able to inhibit oocyte activation induced either by sperm or caffeine. Our present findings provide the first reported evidence of the existence of RyR in frogs. We further explored the relationship between IP₃Rs and RyRs in B. arenarum oocytes by exposing them to the agonists of one class after injecting a blocker of the other class of receptor. We found that thimerosal overcame the inhibitory effect of RyR on oocyte activation, indicating that IP₃Rs function as independent receptors. In contrast, previous injection of heparin delayed caffeine-induced calcium release, revealing a relative dependence of RyRs on functional IP₃Rs, probably through a CICR mechanism. Both receptors play a role in Ca²+ release mechanisms although their relative contribution to the activation process is unclear.

Nitric Oxide-Donor SNAP Induces Xenopus Eggs Activation

“…In fact, RYR are poorly expressed and located near nucleus in Xenopus oocytes. Therefore, the role of RYR is rather considered as modest for endogenous calcium release mechanisms in contrast to pig oocytes [69], [70]. Our results suggest that nitric oxide specifically induces parthenogenetic activation in Xenopus laevis eggs, through a calcium dependent mechanism, though the origin of the calcium changes in our context remains to be determined.…”

Chemical activation inRhinella arenarumoocytes: effect of dehydroleucodine (DhL) and its hydrogenated derivative (2H-DhL)

“…According to the report of Ajmat et al (2011), both heparin and ruthenium red induce inhibition of activation when they are microinjected or added to the culture medium. On the basis of these data, we used the doses with the greatest effect on the activation of this species when added to the culture medium.…”

“…IP 3 induces repetitive or single calcium release in the oocytes of all species studied, while RyR is expressed only in the oocytes of some species. In Rhinella arenarum the presence of RyRs in the oocytes has been described as well as its participation in the process of activation (Ajmat et al , 2011). Results achieved by Ajmat et al (2011, 2013) show that ruthenium red 100 μM and heparin 10 μg/ml in the culture medium as well as the microinjection of ruthenium red 100 μM and heparin 1 μM blocked Ca 2+ output from the intracellular reservoirs in R. arenarum oocytes and strongly inhibited activation induced by insemination with homologous sperm.…”

“…Our laboratory has reported evidence of the existence and functionality of IP 3 Rs and RyRs from in vitro matured R. arenarum oocytes. Both receptors play a role in Ca 2+ release mechanisms during activation of R. arenarum oocytes (Ajmat et al , 2011).…”

Role of phospholipase A2pathway in regulating activation ofBufo arenarumoocytes

“…Our laboratory has previously reported evidence about the existence and functionality of IP 3 Rs and RyRs of in vitro matured Bufo arenarum oocytes. We observed that IP 3 Rs were able to trigger oocyte activation by exerting their effect in an independent manner; by contrast, RyRs-induced oocyte activation showed a relationship between both pathways, probably through a calcium-induced calcium-release (CICR) mechanism (Ajmat et al ., 2010).…”