Arthur G, Sheltawy A
Biochem J. 1980 Nov 1;191(2):523-32. doi: 10.1042/bj1910523.
Lysophosphatidylcholine is thought to be a characteristic component of the chromaffin granules in adrenal glands. By the use of a t.l.c. system that resolves minor phospholipids satisfactorily, this subcellular location was confirmed in the present study in bovine glands. However, phospholipid degradation was demonstrated in homogenates of the adrenal medulla and cortex under conditions similar to those of subcellular fractionation (incubation at 4 degrees C for 90min). Phosphatidylethanolamine and cardiolipin were hydrolysed, but the concentration of lysophosphatidylcholine did not change, indicating that the latter was present in the medulla before this treatment. Attempts were made to decrease the time between death of the animal and the extraction of lipids. Lysophosphatidylcholine was easily demonstrable in lipid extracts of the dissected medulla and even in those of the whole bovine gland. For practical reasons it is not possible to decrease further the time lapse before extraction in the case of this animal. Adrenal glands were obtained from anaesthetized and untreated rabbits. These were frozen immediately in liquid N(2) and the lipids were extracted. In a control experiment, the glands from rabbit were dissected and treated in the same manner as with those of ox, and then the lipids were extracted. No lysophosphatidylcholine was detected in the extracts from glands frozen in liquid N(2) but lysophosphatidylcholine was observed in the controls. These results suggest that lysophosphatidylcholine is not a component of chromaffin granules, but is produced if the period between death of the animal and lipid extraction is unduly prolonged. To discover whether lysophosphatidylcholine affected the permeability barrier properties of chromaffin granules, sonicated liposomes of egg phosphatidylcholine alone or with lysophosphatidylcholine (15mol/100mol) were prepared. Both types were shown by electron microscopy to be largely made up of single bilayer vesicles. The exchange diffusion of [(14)C]dopamine was measured across their membranes. Both types of liposomes had similar capture volumes (0.5mul/mumol of phospholipid), and the activation energies of the exchange diffusion of dopamine were also similar (31kJ/mol). These results indicate that the presence of this proportion of lysophosphatidylcholine in chromaffin-granule membranes is not likely to influence their barrier properties towards catecholamines.
溶血磷脂酰胆碱被认为是肾上腺嗜铬颗粒的一种特征性成分。通过使用一种能令人满意地分离次要磷脂的薄层层析系统，本研究在牛肾上腺中证实了这种亚细胞定位。然而，在类似于亚细胞分级分离的条件下（4℃孵育90分钟），在肾上腺髓质和皮质的匀浆中发现了磷脂降解。磷脂酰乙醇胺和心磷脂被水解，但溶血磷脂酰胆碱的浓度没有变化，这表明在该处理之前它就存在于髓质中。人们试图缩短动物死亡与脂质提取之间的时间。在解剖的髓质的脂质提取物中，甚至在整个牛肾上腺的脂质提取物中都很容易检测到溶血磷脂酰胆碱。出于实际原因，对于这种动物来说，不可能进一步缩短提取前的时间间隔。从麻醉且未处理的兔子身上获取肾上腺。将其立即在液氮中冷冻，然后提取脂质。在一个对照实验中，以与牛肾上腺相同的方式解剖并处理兔子的肾上腺，然后提取脂质。在液氮中冷冻的肾上腺提取物中未检测到溶血磷脂酰胆碱，但在对照中观察到了溶血磷脂酰胆碱。这些结果表明，溶血磷脂酰胆碱不是嗜铬颗粒的成分，而是在动物死亡与脂质提取之间的时间过长时产生的。为了探究溶血磷脂酰胆碱是否会影响嗜铬颗粒的通透性屏障特性，制备了单独的卵磷脂超声脂质体或含有溶血磷脂酰胆碱（15摩尔/100摩尔）的超声脂质体。通过电子显微镜观察，两种类型的脂质体在很大程度上都是由单层双分子层囊泡组成。测量了[(14)C]多巴胺跨其膜的交换扩散。两种类型的脂质体具有相似的捕获体积（0.5微升/微摩尔磷脂），多巴胺交换扩散的活化能也相似（31千焦/摩尔）。这些结果表明，嗜铬颗粒膜中这种比例的溶血磷脂酰胆碱的存在不太可能影响其对儿茶酚胺的屏障特性。
