Zorec R, Hoyland J, Mason W T
Department of Neurobiology, AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, UK.
Pflugers Arch. 1993 Apr;423(1-2):41-50. doi: 10.1007/BF00374959.
The properties of pH and calcium homeostasis have been investigated in single bovine lactotrophs by the use of the fluorescent indicators 2',7'-bis(carboxyethyl)-carboxyfluorescein (BCECF) and fura-2 respectively. A method of simultaneous recording from both dyes loaded in the same cell was used. Despite slight crosstalk between the two dyes, physiologically relevant information about the interrelationship between pH and calcium homeostasis was obtained. Three types of interactions were recorded. First, an increase in calcium due to the discharge of intracellular stores by thyrotropin-releasing hormone resulted in no change in cytosolic pH. Secondly, alkalinization by the addition of a weak base, NH4Cl, induced a large transient (around 1000 nM) and a small (a few tens of nanomoles per liter) sustained increase in cytosolic calcium. The former is partly due to release from agonist-sensitive stores. Thirdly, upon the removal of NH4Cl the cytoplasm became acidic, which induced a release of calcium from intracellular stores in some cells. In addition we demonstrate that the recovery from acid load is sensitive to extracellular Na+, suggesting the presence of Na+/H+ exchange mechanisms in bovine lactotrophs. Interestingly we have also found that, at rest, removal of Na+ from the bathing medium results in a decrease in resting [Ca2+]i, paralleled by a reduction in pHi. This suggests a role for Na+/H+ exchange in determining resting [Ca2+]i.
分别使用荧光指示剂2',7'-双（羧乙基）-羧基荧光素（BCECF）和fura-2，对单个牛催乳细胞的pH值和钙稳态特性进行了研究。采用了一种同时记录加载在同一细胞中的两种染料的方法。尽管两种染料之间存在轻微的串扰，但仍获得了关于pH值与钙稳态之间相互关系的生理相关信息。记录到了三种类型的相互作用。第一，促甲状腺激素释放激素使细胞内储存物质释放导致钙增加，但胞质pH值没有变化。第二，添加弱碱氯化铵进行碱化会引起胞质钙大幅短暂升高（约1000 nM）和小幅持续升高（每升几十纳摩尔）。前者部分归因于激动剂敏感储存物质的释放。第三，去除氯化铵后细胞质变酸，这在一些细胞中会诱导细胞内储存物质释放钙。此外，我们证明酸负荷恢复对细胞外钠离子敏感，这表明牛催乳细胞中存在钠离子/氢离子交换机制。有趣的是，我们还发现，在静息状态下，从浴液中去除钠离子会导致静息胞内钙浓度降低，同时胞内pH值也降低。这表明钠离子/氢离子交换在决定静息胞内钙浓度方面发挥作用。
