title: Participation of inositol trisphosphate and ryanodine receptors in Bufo arenarum oocyte 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.
authors.affiliation: Departamento de Biología del Desarrollo (INSIBIO), Chacabuco 461, 4000-San Miguel de Tucumán, Argentina.
authors.forename: M T
authors.initials: MT
authors.lastname: Ajmat
authors.forename: F
authors.initials: F
authors.lastname: Bonilla
authors.forename: L
authors.initials: L
authors.lastname: Zelarayán
authors.forename: M I
authors.initials: MI
authors.lastname: Bühler
mesh_terms: D000818:Animals; D002022:Bufo arenarum; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism*; D012430:Ruthenium Red / Q000494:pharmacology; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D013084:Sperm-Ovum Interactions; D013849:Thimerosal / Q000494:pharmacology
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D019837:Ryanodine Receptor Calcium Release Channel; D012430:Ruthenium Red; D012433:Ryanodine; D013849:Thimerosal; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium