RyR channel-mediated increase of cytosolic free calcium level signals cyclin B1 degradation during abortive spontaneous egg activation in rat

Abstract

In few mammalian species including rat, post-ovulatory aging induces abortive spontaneous egg activation (SEA), which is morphologically characterized by exit from metaphase-II (M-II) arrest. A possibility exists that the RyR channel-mediated insufficient increase of cytosolic free Ca(2+) level could be one of the causes for post-ovulatory aging-induced abortive SEA. To test this possibility, eggs collected after 17 h post-hCG surge were cultured with or without various concentrations of nifedipine (NF), ruthenium red (RR), and KN-93 for 3 h in vitro. Morphological changes characteristic of abortive SEA, cytosolic free Ca(2+) level, cyclin B1 level, and meiotic status were analyzed. Data of the present study indicate that NF and RR inhibited post-ovulatory aging-induced abortive SEA in a concentration-dependent manner. Further, RR protected against RyR channel as well as caffeine-mediated increase of cytosolic free Ca(2+) level. In addition, KN-93 inhibited post-ovulatory aging-induced abortive SEA in a concentration-dependent manner. An increase of cytosolic free Ca(2+) level was associated with a reduction of cyclin B1 level during post-ovulatory aging-induced abortive SEA. These data indirectly suggest the involvement of RyR channels in the increase of cytosolic free Ca(2+) level. The increased cytosolic free Ca(2+) level triggers cyclin B1 degradation possibly through CaMK-II activity during post-ovulatory aging-induced abortive SEA in rat eggs cultured in vitro.

TRPV4 channels: physiological and pathological role in cardiovascular system

“…However, apart from TRPV4 blocking activity, ruthenium red also possesses the ability to block mitochondrial Ca 2? uniporter [52,94] and ryanodine receptors [68,105]. Accordingly, the cross reactivity of ruthenium red with other targets may possibly contribute to several experimental artifacts.…”

Calcium Signaling During Meiotic Cell Cycle Regulation and Apoptosis in Mammalian Oocytes

“…However, spontaneous oocyte activation (SOA) mimics all characteristics of OA process except formation of pronuclei and extrusion of PB‐II which might be due to insufficient increase of cytosolic free Ca ++ level (Cui et al, ; Premkumar and Chaube, ; Zhang et al, ). Recent studies from our laboratory suggest that insufficient increase of cytosolic free Ca ++ (1.4 times) mediates SOA, while more increase (2.5 times) induced OA in rat oocytes (Premkumar and Chaube, , , ).…”

“…However, in some mammalian species, if fertilization does not occur, postovulatory oocyte aging mediates spontaneous exit from M‐II arrest by inducing the initiation of extrusion of second polar body (PB‐II) (Premkumar and Chaube, , ). The PB‐II does not get completely extruded and ovulated oocytes are further arrested at metaphase‐III (M‐III) like stage without forming pronuclei (Chebotareva et al, ; Premkumar and Chaube, , ; Prasad et al, ,, ,).…”

“…Growing body of evidences suggest that Ca ++ modulates oocyte physiology depending upon its intracellular Ca ++ ([Ca ++ ]i) concentration (Homa, ; Tosti, ; Whitaker, ; Naik and Pardasani, ). For instance, a transient increase of [Ca ++ ]i under physiological range triggers spontaneous exit from diplotene arrest (Fan et al, ; Chaube et al, ; Pandey et al, ) as well as M‐II arrest (Vincent et al, ; Ruddock et al, ; Lu et al, ; Chaube et al, ; Premkumar and Chaube, , ). The sustained high level beyond physiological range results in meiotic cell cycle arrest and then apoptosis (Homa et al, ; Berridge et al, ; Tripathi et al, , , , , ; Zhang and Fissore, ; Tiwari et al, ).…”

“…Drugs that trigger Ca ++ release from internal stores increases cytosolic free Ca ++ level and induce OA in mouse (Vincent et al, ), rat (Raz et al, ), porcine (Ruddock et al, ; Ito et al, ), and human oocytes under in vitro culture conditions (Sengoku et al, ). On the other hand, use of nifedipine and ruthenium red in culture medium can protect oocytes undergoing postovulatory aging‐induced SOA to increase the number of M‐II arrested oocytes required for various assisted reproductive technology (ART) program (Yoo and Smith, ; Premkumar and Chaube, ). The Ca ++ channel blockers such as verapamil inhibit spontaneous meiotic resumption in mouse (Homa, ), rat (Paleos and Powers, ; Chaube et al, ), bovine (Tosti et al, ), and porcine oocytes (Bae and Channing, ; Rozinek et al, ).…”