Medical School, University of Birmingham, Birmingham B15 2TT, UK.
Biochem J. 2012 Dec 1;448(2):189-200. doi: 10.1042/BJ20120339.
Ca2+i signalling is pivotal to sperm function. Progesterone, the best-characterized agonist of human sperm Ca2+i signalling, stimulates a biphasic [Ca2+]i rise, comprising a transient and subsequent sustained phase. In accordance with recent reports that progesterone directly activates CatSper, the [Ca2+]i transient was detectable in the anterior flagellum (where CatSper is expressed) 1-2 s before responses in the head and neck. Pre-treatment with 5 μM 2-APB (2-aminoethoxydiphenyl borate), which enhances activity of store-operated channel proteins (Orai) by facilitating interaction with their activator [STIM (stromal interaction molecule)] 'amplified' progesterone-induced [Ca2+]i transients at the sperm neck/midpiece without modifying kinetics. The flagellar [Ca2+]i response was unchanged. 2-APB (5 μM) also enhanced the sustained response in the midpiece, possibly reflecting mitochondrial Ca2+ accumulation downstream of the potentiated [Ca2+]i transient. Pre-treatment with 50-100 μM 2-APB failed to potentiate the transient and suppressed sustained [Ca2+]i elevation. When applied during the [Ca2+]i plateau, 50-100 μM 2-APB caused a transient fall in [Ca2+]i, which then recovered despite the continued presence of 2-APB. Loperamide (a chemically different store-operated channel agonist) enhanced the progesterone-induced [Ca2+]i signal and potentiated progesterone-induced hyperactivated motility. Neither 2-APB nor loperamide raised pHi (which would activate CatSper) and both compounds inhibited CatSper currents. STIM and Orai were detected and localized primarily to the neck/midpiece and acrosome where Ca2+ stores are present and the effects of 2-APB are focussed, but store-operated currents could not be detected in human sperm. We propose that 2-APB-sensitive channels amplify [Ca2+]i elevation induced by progesterone (and other CatSper agonists), amplifying, propagating and providing spatio-temporal complexity in [Ca2+]i signals of human sperm.
钙离子信号对于精子功能至关重要。孕激素是人类精子钙离子信号的最佳激动剂，它刺激双相钙离子升高，包括短暂和随后的持续阶段。根据最近的报道，孕激素直接激活 CatSper，钙离子瞬变可在前部鞭毛（CatSper 表达的地方）中检测到，比头部和颈部的反应早 1-2 秒。用 5 μM 2-APB（2-氨基乙氧基二苯硼酸盐）预处理可增强储存操作通道蛋白（Orai）的活性，通过促进其激活剂[STIM（基质相互作用分子）]的相互作用来增强钙库操作通道蛋白的活性，从而放大孕激素诱导的钙离子瞬变在精子颈/中段而不改变动力学。鞭毛钙离子反应没有改变。2-APB（5 μM）也增强了中段的持续反应，可能反映了增强的钙离子瞬变下游的线粒体钙离子积累。用 50-100 μM 2-APB 预处理不能增强瞬变并抑制持续钙离子升高。当在钙离子平台期应用时，50-100 μM 2-APB 导致钙离子瞬态下降，尽管继续存在 2-APB，但钙离子随后恢复。洛哌丁胺（一种化学不同的储存操作通道激动剂）增强了孕激素诱导的钙离子信号，并增强了孕激素诱导的超激活运动。2-APB 和洛哌丁胺都没有提高 pH 值（这会激活 CatSper），并且这两种化合物都抑制了 CatSper 电流。STIM 和 Orai 被检测到并主要定位于颈部/中段和顶体，那里存在钙离子储存库，2-APB 的作用集中，但在人类精子中无法检测到储存操作电流。我们提出，2-APB 敏感通道放大孕激素（和其他 CatSper 激动剂）诱导的钙离子升高，放大、传播并提供人类精子钙离子信号的时空复杂性。
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