Perry J W, Oka T
Biochim Biophys Acta. 1980 Apr 17;629(1):24-35. doi: 10.1016/0304-4165(80)90261-5.
The biphasic increase of ornithine decarboxylase activity in mouse mammary gland in organ culture occurs with a hormone-independent first peak and a hormone-dependent second peak. The data presented indicate that a change in the osmolarity of the cellular environment is the major contributing factor for the emergence of the hormone-independent ornithine decarboxylase activity in mammary explants. Thus, incubation of mammary explants for 3 h in a medium diluted 53% with distilled water results in approx. 1000-fold stimulation of enzyme activity over the initial level, whereas a similar dilution of the medium with 0.18 M NaCl or 0.3 M sucrose blocks the increase. The increase in enzyme activity is similarly affected by a reduction of the concentration of NaCl in the culture medium. The hypoosmotic stimulation of ornithine decarboxylase activity appears to be affected at a posttranscriptional level, and is enhanced further by the actions of insulin and prolactin. The hypoosmotic enhancement of ornithine decarboxylase activity produces a large increase in the intracellular concentration of putrescine in mammary explants. However, neither the concentration of spermidine and spermine nor the activity of S-adenosyl-L-methionine decarboxylase is affected. In addition, studies of putrescine transport in mammary explants show that hypotonicity causes an increase in the rate of influx and a decrease in efflux of putrescine with enhancement of intracellular putrescine accumulation. On the other hand, the uptake of spermidine, spermine, amino acids, sugar, and a lipophilic cation, triphenylmethylphosphonium is unaffected. These data suggest a possibility that osmotic alteration in cellular environment causes an incresed need for putrescine in mammary cells, resulting in stimulation of ornithine decarboxylase activity, which may represent a cellular mechanism for maintaining the homeostasis of the intracellular cationic environment.
在器官培养中，小鼠乳腺中鸟氨酸脱羧酶活性呈双相增加，第一个峰值不依赖激素，第二个峰值依赖激素。所呈现的数据表明，细胞环境渗透压的变化是乳腺外植体中出现不依赖激素的鸟氨酸脱羧酶活性的主要促成因素。因此，将乳腺外植体在用蒸馏水稀释53%的培养基中孵育3小时，会导致酶活性比初始水平提高约1000倍，而用0.18 M NaCl或0.3 M蔗糖对培养基进行类似稀释则会阻止这种增加。培养基中NaCl浓度的降低对酶活性的增加有类似影响。鸟氨酸脱羧酶活性的低渗刺激似乎在转录后水平受到影响，并且胰岛素和催乳素的作用会进一步增强这种刺激。鸟氨酸脱羧酶活性的低渗增强导致乳腺外植体中腐胺的细胞内浓度大幅增加。然而，亚精胺和精胺的浓度以及S-腺苷-L-甲硫氨酸脱羧酶的活性均未受到影响。此外，对乳腺外植体中腐胺转运的研究表明，低渗会导致腐胺流入速率增加和流出速率降低，同时细胞内腐胺积累增加。另一方面，亚精胺、精胺、氨基酸、糖和一种亲脂性阳离子三苯甲基鏻的摄取不受影响。这些数据表明，细胞环境中的渗透压改变可能导致乳腺细胞对腐胺的需求增加，从而刺激鸟氨酸脱羧酶活性，这可能代表了一种维持细胞内阳离子环境稳态的细胞机制。
