Baer H P, Vriend R
J Pharmacol Exp Ther. 1984 May;229(2):564-70.
Attempts were made to measure adenosine transport in isolated smooth muscle preparations including guinea-pig taenia caeci, beef coronary arteries and longitudinal muscle of rabbit small intestine. Because adenosine-mediated relaxation is potentiated by nucleoside transport inhibitors such as dipyridamole and 6- thiobenzylpurine ribosides in the first two systems but not in rabbit intestinal muscle, possible differences in transport capacities and in the effects of these inhibitors in the three tissues were examined. Transport was to be measured by assessing metabolic products of adenosine including adenine nucleotides and inosine plus hypoxanthine in both tissues and incubation media. Despite extensive rinsing of tissues, adenosine deaminase leaked into the incubation media, requiring its inhibition by 5 nM deoxycoformycin. When measuring apparent transport rates by quantitating metabolic products in the presence of 5 nM deoxycoformycin, no saturation of uptake at 100 to 400 microM adenosine was observed in taenia caeci and rabbit muscle. Comparing these results with literature reports on transport rates in single cell preparations, it appears that the obtained values (20-40 pmol/mg/min) may be at least 100-fold lower, suggesting that rates of diffusion through tissue and intracellular deamination of adenosine were the limiting functions measured by the methodology used in this study, requiring a careful definition for the terms transport and uptake and suggesting that it is practically not possible to measure true transport of adenosine in intact tissues. The uptake of adenosine was inhibited in all three tissues by dipyridamole and 6- thiobenzylpurine ribosides (10 microM) to a similar extent, leaving open the question of why potentiation of the relaxant effects of adenosine is seen in taenia caeci and coronary arteries but not in rabbit intestinal muscle.
研究人员尝试在分离的平滑肌制剂中测量腺苷转运，这些制剂包括豚鼠盲肠带、牛冠状动脉和兔小肠纵肌。由于在前两个系统中，腺苷介导的舒张作用会被核苷转运抑制剂如双嘧达莫和6-硫代苄基嘌呤核苷增强，但在兔肠肌中则不然，因此研究了这三种组织在转运能力以及这些抑制剂作用方面可能存在的差异。通过评估腺苷的代谢产物（包括腺嘌呤核苷酸、肌苷和次黄嘌呤）在组织和孵育介质中的含量来测量转运。尽管对组织进行了广泛冲洗，但腺苷脱氨酶仍会泄漏到孵育介质中，因此需要用5 nM脱氧助间型霉素对其进行抑制。当在存在5 nM脱氧助间型霉素的情况下通过定量代谢产物来测量表观转运速率时，在盲肠带和兔肌肉中，100至400 microM腺苷的摄取未出现饱和现象。将这些结果与单细胞制剂中转运速率的文献报道进行比较，发现所获得的值（20 - 40 pmol/mg/min）可能至少低100倍，这表明通过组织的扩散速率和腺苷的细胞内脱氨作用是本研究方法所测量的限制因素，这需要对转运和摄取这两个术语进行仔细定义，同时也表明在完整组织中实际不可能测量到腺苷的真正转运。双嘧达莫和6-硫代苄基嘌呤核苷（10 microM）在所有三种组织中对腺苷摄取的抑制程度相似，这就留下了一个问题：为什么在盲肠带和冠状动脉中能看到腺苷舒张作用的增强，而在兔肠肌中却没有。
