Hyne R V
Biol Reprod. 1984 Sep;31(2):312-23. doi: 10.1095/biolreprod31.2.312.
The monovalent cationic ionophores monensin and nigericin stimulated rapid guinea pig sperm acrosome reactions in the presence of extracellular Na+, Ca2+ and bicarbonate (HCO3-/CO2). Extracellular K+ (mM concentrations), in contrast, was not required for the stimulatory effect of the ionophores. The effect of HCO3-/CO2 is concentration, pH and temperature dependent, with maximal responses obtained with 50 microM monensin or 25 microM nigericin at a concentration of 30 mM HCO3-, 2.5% CO2 and pH 7.8 at 25 degrees C. At a constant HCO3- concentration (30 mM), monensin stimulated acrosome reactions within the pH range 7.5-7.8, whereas a higher or lower pH did not support acrosome reactions at 25 degrees C. At constant extracellular pH (7.8), monensin stimulated acrosome reactions in the presence of 30 mM HCO3-, whereas higher and lower concentrations did not support acrosome reactions at 25 degrees C. The permeant anions pyruvate and lactate were essential to maintain sperm motility when treated with monensin under these conditions. NH4Cl, sodium acetate and 4,41-diisothiocyano-2, 21-disulfonic acid stibene (DIDS; 25 microM), an anion transport inhibitor, blocked the ability of monensin to stimulate acrosome reactions. Verapamil (100 microM), a putative Ca2+ transport antagonist, in contrast, did not prevent the monensin-induced acrosome reactions. Physiological concentrations of Na+ were needed for monensin to stimulate acrosome reactions, but high concentrations of Mg2+ prevented the monensin stimulation. The Ca2+ ionophore A23187 (75 nM) also required physiological concentrations of Na+ for the rapid induction of maximal acrosome reactions at an elevated pH (8.3) but did not require the presence of extracellular HCO3-. These studies suggest that a monovalent ionophore-induced rise in sperm intracellular Na+ concentrations is a pre-Ca2+ entry event, that stimulates an endogenous Ca2+/Na+ exchange that allows a Ca2+ influx which in turn induces the acrosome reaction. The possible regulatory role of the sperm intracellular pH and Na+, K+-ATPase during the capacitation process under physiological conditions is discussed.
单价阳离子载体莫能菌素和尼日利亚菌素在细胞外存在Na⁺、Ca²⁺和碳酸氢盐（HCO₃⁻/CO₂）的情况下，能刺激豚鼠精子快速发生顶体反应。相比之下，离子载体发挥刺激作用并不需要细胞外K⁺（毫摩尔浓度）。HCO₃⁻/CO₂的作用取决于浓度、pH值和温度，在25℃下，当HCO₃⁻浓度为30 mM、CO₂浓度为2.5%、pH值为7.8时，50 μM莫能菌素或25 μM尼日利亚菌素可产生最大反应。在HCO₃⁻浓度恒定（30 mM）时，莫能菌素在pH值7.5 - 7.8范围内刺激顶体反应，而在25℃时，更高或更低的pH值均不支持顶体反应。在细胞外pH值恒定（7.8）时，莫能菌素在30 mM HCO₃⁻存在的情况下刺激顶体反应，而在25℃时，更高和更低的浓度均不支持顶体反应。在这些条件下，用莫能菌素处理时，渗透性阴离子丙酮酸和乳酸对于维持精子活力至关重要。NH₄Cl、醋酸钠和阴离子转运抑制剂4,4'-二异硫氰酸根合-2,2'-二磺酸芪（DIDS；25 μM）可阻断莫能菌素刺激顶体反应的能力。相比之下，维拉帕米（100 μM），一种假定的Ca²⁺转运拮抗剂，不能阻止莫能菌素诱导的顶体反应。莫能菌素刺激顶体反应需要生理浓度的Na⁺，但高浓度的Mg²⁺会阻止莫能菌素的刺激作用。Ca²⁺离子载体A23187（75 nM）在pH值升高（8.3）时快速诱导最大顶体反应也需要生理浓度的Na⁺，但不需要细胞外HCO₃⁻的存在。这些研究表明，单价离子载体诱导的精子细胞内Na⁺浓度升高是Ca²⁺进入之前的一个事件，它刺激内源性Ca²⁺/Na⁺交换，使Ca²⁺内流，进而诱导顶体反应。本文还讨论了生理条件下精子细胞内pH值以及Na⁺、K⁺-ATP酶在获能过程中可能的调节作用。
