Extracellular calcium is required for intracellular Ca²⁺ oscillations needed for egg activation, but the regulatory mechanism is still poorly understood. The present study was designed to demonstrate the function of calcium‐sensing receptor (CASR), which could recognize extracellular calcium as first messenger, during porcine egg activation. CASR expression was markedly upregulated following egg activation. Functionally, the addition of CASR agonist NPS R‐568 significantly enhanced pronuclear formation rate, while supplementation of CASR antagonist NPS2390 compromised egg activation. There was no change in NPS R‐568 group compared with control group when the egg activation was performed without extracellular calcium addition. The addition of NPS2390 precluded the activation‐dependent [Ca²⁺]_i rise. When egg activation was conducted in intracellular Ca²⁺ chelator BAPTA‐AM and NPS R‐568 containing medium, CASR function was abolished. Meanwhile, CASR activation increased the level of the [Ca²⁺]_i effector p‐CAMKII, and the presence of KN‐93, an inhibitor of CAMKII, significantly reduced the CASR‐mediated increasement of pronuclear formation rate. Furthermore, the increase of CASR expression following activation was reversed by inhibiting CAMKII activity, supporting a positive feedback loop between CAMKII and CASR. Altogether, these findings provide a new pathway of egg activation about CASR, as the extracellular Ca²⁺ effector, promotes egg activation via its downstream effector and upstream regulator CAMKII.

中文翻译：

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细胞外钙敏感受体通过钙/钙调蛋白依赖性蛋白激酶II促进猪卵活化。

卵激活所需的细胞内Ca ²⁺振荡需要细胞外钙，但调节机制仍知之甚少。本研究旨在证明钙敏感受体（CASR）的功能，该受体可以在猪卵活化过程中将细胞外钙识别为第一信使。卵激活后，CASR表达明显上调。从功能上讲，添加CASR激动剂NPS R-568可显着提高前核形成率，而补充CASR拮抗剂NPS2390则可破坏卵的活化。在不添加细胞外钙的情况下进行蛋活化的情况下，NPS R-568组与对照组相比没有变化。NPS2390的添加排除了依赖激活的[Ca ²⁺]_我上升。当在细胞内Ca ²⁺螯合剂BAPTA-AM和NPS R-568所含培养基中进行卵活化时，CASR功能被取消。同时，CASR激活增加了[Ca ²⁺ ] _i效应物p-CAMKII的水平，而CAMKII抑制剂KN-93的存在显着降低了CASR介导的前核形成率的增加。此外，激活后CASR表达的增加通过抑制CAMKII活性而逆转，支持CAMKII和CASR之间的正反馈回路。总之，这些发现为CASR提供了卵活化的新途径，因为细胞外Ca ²⁺ 效应子通过其下游效应子和上游调节剂CAMKII促进卵子活化。