Allemand D, de Renzis G, Girard J P, Payan P
Exp Cell Res. 1987 Mar;169(1):169-77. doi: 10.1016/0014-4827(87)90235-7.
The comparative importance of the release of intracellular ionic calcium, Na+/H+ exchange and cytosolic alkalosis as activator signals was studied on the development of amino acid uptake at fertilization in sea urchin eggs. We show that, once stimulated, the rate of valine uptake is greatly dependent upon intracellular pH. Suppression of the Na+/H+ exchange at the time of activation, by applying ionophore (A23187) in sodium-free artificial sea water (ONaASW), inhibits the development of valine influx. This cannot be restored by a further (30 min later) alkalosis by transferring eggs into sea water. Suppressing the alkalosis in the presence of Na+/H+ exchange at fertilization by simultaneous addition of acid into sea water results in activation of the amino acid carrier which exhibits an increased rate of transport as soon as the eggs are replaced in sea water at pH 8.0. The absence of alkalosis in eggs activated in ONaASW can be counterbalanced either by adding NH4Cl 10 mM or by transfer into ASW at pH 9.0 at activation. Ammonia-treated eggs absorbed amino acid as controls, whereas eggs in sea water at pH 9.0 failed to develop a valine uptake system, suggesting that ammonia can completely replace the effect of Na+/H+ exchange. Furthermore, addition of NH4Cl immediately before fertilization conceals the Na+/H+ exchange but stimulates valine uptake as in controls. These data suggest that: the occurrence of the intracellular calcium increase alone is not sufficient for the develpment of the amino acid transport system; cell alkalinization at fertilization derives from the cytoplasmic membrane-located Na+/H+ exchange and an inward movement of protons into a cortical acidic compartment, which is discussed.
我们研究了细胞内离子钙释放、Na⁺/H⁺交换和胞质碱化作为激活信号在海胆卵受精时氨基酸摄取发育过程中的相对重要性。我们发现，一旦受到刺激，缬氨酸摄取速率在很大程度上取决于细胞内pH值。在无钠人工海水（ONaASW）中应用离子载体（A23187）抑制激活时的Na⁺/H⁺交换，会抑制缬氨酸内流的发育。在激活30分钟后将卵转移到海水中，进一步的碱化并不能恢复这种抑制。在受精时通过同时向海水中添加酸来抑制Na⁺/H⁺交换存在时的碱化，会激活氨基酸载体，一旦将卵置于pH 8.0的海水中，该载体的转运速率就会增加。在ONaASW中激活的卵中碱化的缺失可以通过添加10 mM氯化铵或在激活时转移到pH 9.0的人工海水（ASW）中来抵消。经氨处理的卵像对照一样吸收氨基酸，而pH 9.0海水中的卵未能发育出缬氨酸摄取系统，这表明氨可以完全替代Na⁺/H⁺交换的作用。此外，在受精前立即添加氯化铵会掩盖Na⁺/H⁺交换，但会像对照一样刺激缬氨酸摄取。这些数据表明：仅细胞内钙增加的发生不足以使氨基酸转运系统发育；受精时的细胞碱化源于位于细胞质膜的Na⁺/H⁺交换以及质子向皮质酸性区室的内向移动，对此进行了讨论。
