Schaefer M, Hofmann T, Schultz G, Gudermann T
Institut fur Pharmakologie, Freie Universitat Berlin, Thielallee 67-73, D-14195 Berlin, Germany.
Proc Natl Acad Sci U S A. 1998 Mar 17;95(6):3008-13. doi: 10.1073/pnas.95.6.3008.
Zona pellucida protein 3, a protein of the egg's extracellular matrix, and progesterone secreted by granulosa cells surrounding the oocyte are regarded as physiological stimuli of sperm acrosome reaction. Signal transduction steps initiated by both stimuli result in influx of Ca2+ from the extracellular space. Herein, we propose a role for prostaglandin (PG) E as a physiological inducer of Ca2+ influx and acrosome reaction in human spermatozoa. PGE1 specifically binds to human sperm membranes (Kd = 20.4 nM; Bmax = 88 fmol/mg protein) and induces a pertussis toxin-insensitive, transient increase in intracellular Ca2+ concentrations, which can be blocked by microM concentrations of La3+, Gd3+, and Zn2+. The kinetic profile was similar to that observed after progesterone challenge. Sequential application of both agonists did not lead to cross-desensitization. E prostaglandins were found to be the only prostanoids with agonistic properties (EC50 values for PGE1 and PGE2: <10 nM and 300 nM, respectively). Pharmacological characteristics were not compatible with those of cloned prostanoid receptors indicating the expression of a distinct membrane receptor. Activation of the sperm E prostanoid receptor stimulates incorporation of [alpha-32P]GTP azidoanilide into immunoprecipitated Galphaq/11 subunits. Thus, in human sperm, PG induces Ca2+ influx and acrosome reaction via a Gq/11-coupled E prostanoid receptor. The block of PGE1-induced Ca2+ transients and acrosome reaction by physiological Zn2+ concentrations highlights a role of Zn2+ as an endogenous Ca2+ channel blocker present in seminal plasma protecting sperm from premature PGE1-evoked increases in intracellular Ca2+ concentrations.
透明带蛋白3是卵子细胞外基质中的一种蛋白质，由卵母细胞周围的颗粒细胞分泌的孕酮被视为精子顶体反应的生理刺激物。这两种刺激引发的信号转导步骤都会导致细胞外空间的Ca2+内流。在此，我们提出前列腺素（PG）E作为人类精子中Ca2+内流和顶体反应的生理诱导剂的作用。PGE1特异性结合人类精子膜（Kd = 20.4 nM；Bmax = 88 fmol/mg蛋白质），并诱导百日咳毒素不敏感的细胞内Ca2+浓度瞬时升高，这可被微摩尔浓度的La3+、Gd3+和Zn2+阻断。动力学曲线与孕酮刺激后观察到的相似。两种激动剂的顺序应用不会导致交叉脱敏。发现E型前列腺素是唯一具有激动特性的前列腺素（PGE1和PGE2的EC50值分别为<10 nM和300 nM）。药理学特性与克隆的前列腺素受体不相符，表明存在一种独特的膜受体。精子E型前列腺素受体的激活刺激[α-32P]GTP叠氮苯胺掺入免疫沉淀的Gαq/11亚基。因此，在人类精子中，PG通过Gq/11偶联的E型前列腺素受体诱导Ca2+内流和顶体反应。生理浓度的Zn2+对PGE1诱导的Ca2+瞬变和顶体反应的阻断突出了Zn2+作为精浆中存在的内源性Ca2+通道阻滞剂的作用，可保护精子免受PGE1过早引起的细胞内Ca2+浓度升高的影响。
