Kather H
Klinisches Institut für Herzinfarktforschung, Medizinische Universitätsklinik Heidelberg, West Germany.
J Biol Chem. 1988 Jun 25;263(18):8803-9.
Human adipocytes are of limited viability (7 +/- 2% release of lactate dehydrogenase/h) and contain active ectophosphatases which are capable of sequentially degrading ATP to adenosine. At densities of 30,000-40,000 cells/ml, human fat cell suspensions accumulated adenosine, inosine, and hypoxanthine, and their concentrations were 38 +/- 8, 120 +/- 10, and 31 +/- 7 nmol/liter after 3 h of incubation. Dipyridamole (10 mumol/liter), an inhibitor of nucleoside transport, caused a 5-7-fold increase in adenosine accumulation which was reduced by 85% on inhibition of ectophosphatases by beta-glycerophosphate and antibodies against ecto-5'-nucleotidase or alpha, beta-methylene 5'-adenosine diphosphate (10 mumol/liter), respectively, indicating that most of the adenosine is produced in the extracellular compartment. Accordingly, the spontaneous accumulation of adenosine was reduced beyond 5 nmol/liter on inhibition of ectophosphatase activities or removal of extracellular AMP by AMP deaminase (4 units/ml). Added adenosine (30 nmol/liter) disappeared until its concentration approached 5 nmol/liter. Isoproterenol (1 mumol/liter) had no effect on adenosine accumulation regardless whether purine production from extracellular sources was minimized or not. In contrast to adenosine, the concentrations of inosine and hypoxanthine displayed only a modest decrease (30-50%) on inhibition of ectophosphatase activities. In addition, isoproterenol caused a 2-3-fold increase in inosine and hypoxanthine production which was concentration-dependent and could be inhibited by propranolol. It is concluded that the adenosine that accumulates in human adipocyte suspensions is almost exclusively derived from adenine nucleotides which are released by leaking cells. By contrast, inosine and hypoxanthine are produced inside the cells, and the release of these latter purines appears to be linked to ATP turnover via adenylate cyclase.
人脂肪细胞的活力有限（乳酸脱氢酶每小时释放7±2%），且含有活性胞外磷酸酶，这些酶能够将ATP依次降解为腺苷。在细胞密度为30000 - 40000个/毫升时，人脂肪细胞悬液会积累腺苷、肌苷和次黄嘌呤，孵育3小时后它们的浓度分别为38±8、120±10和31±7纳摩尔/升。双嘧达莫（10微摩尔/升），一种核苷转运抑制剂，可使腺苷积累增加5 - 7倍，而当分别用β - 甘油磷酸酯以及抗胞外5'-核苷酸酶或α,β - 亚甲基5'-腺苷二磷酸（10微摩尔/升）的抗体抑制胞外磷酸酶时，腺苷积累量减少85%，这表明大部分腺苷是在细胞外间隙产生的。因此，抑制胞外磷酸酶活性或用AMP脱氨酶（4单位/毫升）去除细胞外AMP后，腺苷的自发积累量降至5纳摩尔/升以下。添加的腺苷（30纳摩尔/升）会逐渐消失，直至其浓度接近5纳摩尔/升。异丙肾上腺素（1微摩尔/升）对腺苷积累没有影响，无论细胞外来源的嘌呤生成是否降至最低。与腺苷不同，抑制胞外磷酸酶活性时，肌苷和次黄嘌呤的浓度仅适度降低（30 - 50%）。此外，异丙肾上腺素可使肌苷和次黄嘌呤的生成增加2 - 3倍，且具有浓度依赖性，可被普萘洛尔抑制。结论是人脂肪细胞悬液中积累的腺苷几乎完全来源于渗漏细胞释放的腺嘌呤核苷酸。相比之下，肌苷和次黄嘌呤是在细胞内产生的，这些嘌呤的释放似乎与通过腺苷酸环化酶的ATP周转有关。
