Reimers H J, Mustard J F, Packham M A
J Cell Biol. 1975 Oct;67(1):61-71. doi: 10.1083/jcb.67.1.61.
The metabolic pool of adenine nucleotides in platelets can be labeled by incubating platelets for 1 h in vitro with [14C]adenosine or [32P]orthophosphate. When these platelets are treated with thrombin, the adenine nucleotides released are not labeled. Because of this, Holmsen's suggestion of a metabolically inert pool of granule nucleotides has been generally accepted. We have found that upon incubation of labeled rabbit platelets for longer times (up to 6 h) in vitro, or upon reinjection and reharvesting at times up to 66 h, the releasable pool of adenine nucleotides becomes labeled. Because the rates of 32p and 14C incorporation into this releasable pool are similar, it seems likely that these labels enter the granules as ATP. Equilibrium between the metabolic and granule pools is complete by 18 h. When rabbit platelets are labeled in vivo by intravenous injection of [32P]orthophosphate, peak labeling occurs between 60 and 70 h; this corresponds to their maturation time. The platelets probably incorporate 32P during their production in the megakaryocytes. The specific radioactivity of the adenine nucleotides in the releasable (granule) pool of these platelets is the same as the specific radioactivity in the nonreleasable (metabolic) pool. Since inorganic phosphate in platelets (and undoubtedly in the megakaryocytes) exchanges with inorganic phosphate in plasma, and since the radioactivity of the latter decreases rapidly, the adenine nucleotides in the two pools must exchange to maintain the same specific radioactivity. Transfer of adenine nucleotides into storage granules may represent a general phenomenon because it has been observed in the chromaffin cells of the adrenal medulla also.
血小板中腺嘌呤核苷酸的代谢池可通过将血小板与[14C]腺苷或[32P]正磷酸盐在体外孵育1小时来标记。当用凝血酶处理这些血小板时，释放出的腺嘌呤核苷酸未被标记。因此，霍尔姆森提出的颗粒核苷酸代谢惰性池的观点已被普遍接受。我们发现，将标记的兔血小板在体外孵育更长时间（长达6小时），或在长达66小时的时间点进行再注射和重新收获时，腺嘌呤核苷酸的可释放池会被标记。由于32P和14C掺入这个可释放池的速率相似，这些标记似乎是以ATP的形式进入颗粒的。代谢池和颗粒池之间在18小时时达到平衡。当通过静脉注射[32P]正磷酸盐在体内标记兔血小板时，在60至70小时之间出现标记峰值；这与它们的成熟时间相对应。血小板可能在巨核细胞中产生过程中掺入32P。这些血小板可释放（颗粒）池中腺嘌呤核苷酸的比放射性与不可释放（代谢）池中的比放射性相同。由于血小板（无疑还有巨核细胞）中的无机磷酸盐与血浆中的无机磷酸盐进行交换，且后者的放射性迅速降低，两个池中的腺嘌呤核苷酸必须进行交换以维持相同的比放射性。腺嘌呤核苷酸向储存颗粒的转移可能是一种普遍现象，因为在肾上腺髓质的嗜铬细胞中也观察到了这种现象。
