McDaniel M L, Weaver D C, Roth C E, Fink C J, Swanson J A, Lacy P E
Endocrinology. 1977 Dec;101(6):1701-8. doi: 10.1210/endo-101-6-1701.
The uptake of theophylline and caffeine was determined in isolated pancreatic islets employing a dual isotope procedure with sucrose as an extracellular marker. Islets rapidly accumulated caffeine and theophylline with apparent dissociation constants of approximately 23 and 6 mM, respectively. Theophylline inhibited the uptake of caffeine and caused displacement of caffein from islets. These results indicated a competition by theophylline and caffeine for a common site (binding and/or transport carrier). In addition, theophylline and caffeine inhibited D-glucose transport in a dose-dependent manner and within the limits of the experimental system, this inhibition appeared to be non-competitive. (Bu)2cAMP under similar experimental conditions exerted no effect on D-glucose transport. These results present evidence for a rapid uptake of theophylline and caffeine in pancreatic islets, which is compatible with their immediate cellular effects. In addition, these results demonstrate a direct effect by theophylline and caffeine on D-glucose transport which appears independent of their ability to alter intracellular cAMP levels.
采用以蔗糖作为细胞外标志物的双同位素程序，在分离的胰岛中测定了茶碱和咖啡因的摄取情况。胰岛迅速积累咖啡因和茶碱，其表观解离常数分别约为23 mM和6 mM。茶碱抑制咖啡因的摄取，并导致咖啡因从胰岛中被置换出来。这些结果表明茶碱和咖啡因竞争一个共同位点（结合和/或转运载体）。此外，茶碱和咖啡因以剂量依赖的方式抑制D-葡萄糖转运，并且在实验系统的范围内，这种抑制似乎是非竞争性的。在类似实验条件下，(Bu)2cAMP对D-葡萄糖转运没有影响。这些结果提供了证据，证明茶碱和咖啡因在胰岛中迅速摄取，这与其即时的细胞效应相符。此外，这些结果表明茶碱和咖啡因对D-葡萄糖转运有直接作用，这种作用似乎与其改变细胞内cAMP水平的能力无关。
