Ravid K, Lowenstein J M
Graduate Department of Biochemistry, Brandeis University, Waltham, MA 02254.
Biochem J. 1988 Jan 15;249(2):377-81. doi: 10.1042/bj2490377.
Incubation of undifferentiated 3T3-F442A cells (preadipocytes) with 5'-N-ethylcarboxamidoadenosine (NECA) increases intracellular cyclic AMP in a dose-dependent manner. The effect of NECA is antagonized by 8-phenyltheophylline, but potentiated by 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidine, an inhibitor of cyclic AMP phosphodiesterase. Incubation of preadipocytes with (-)-N6-(R-phenylisopropyl)adenosine (PIA) has no inhibitory effect on the basal concentration of cyclic AMP or on the stimulation of adenylate cyclase by isoprenaline or forskolin. Micromolar concentrations of PIA increase intracellular cyclic AMP, but with a lower potency than NECA. Similar findings are obtained with the non-differentiating cell line 3T3-C2. Thus preadipocyte 3T3-F442A cells and 3T3-C2 cells appear to express only stimulatory adenosine receptors. For some time after 3T3-F442A cells have differentiated to adipocytes, micromolar concentrations of NECA and PIA continue to increase cyclic AMP to a similar extent to that in preadipocytes, whereas nanomolar concentrations of PIA decrease the stimulatory effects of isoprenaline and forskolin on adenylate cyclase by 50%. However, several days after differentiation, the adipocytes gradually lose the major part of their positive response to NECA and reach a steady response to NECA 10 days after differentiation. The inhibition of adenylate cyclase caused by PIA remains constant for at least 2 weeks after differentiation. With membranes derived from the cells, the effects of NECA and PIA depend on GTP. These results indicate that, during the differentiation of 3T3-F442A cells to adipocytes, new inhibitory adenosine receptors are expressed, whereas the stimulatory receptors become attenuated.
将未分化的3T3-F442A细胞（前脂肪细胞）与5'-N-乙基羧酰胺腺苷（NECA）一起孵育，细胞内的环磷酸腺苷（cAMP）会以剂量依赖的方式增加。NECA的作用可被8-苯基茶碱拮抗，但可被环磷酸腺苷磷酸二酯酶抑制剂4-(3-丁氧基-4-甲氧基苄基)-2-咪唑烷增强。将前脂肪细胞与(-)-N6-(R-苯异丙基)腺苷（PIA）一起孵育，对cAMP的基础浓度或异丙肾上腺素或福斯高林对腺苷酸环化酶的刺激均无抑制作用。微摩尔浓度的PIA可增加细胞内的cAMP，但效力低于NECA。在未分化的细胞系3T3-C2中也得到了类似的结果。因此，前脂肪细胞3T3-F442A细胞和3T3-C2细胞似乎只表达刺激性腺苷受体。在3T3-F442A细胞分化为脂肪细胞后的一段时间内，微摩尔浓度的NECA和PIA继续以与前脂肪细胞相似的程度增加cAMP，而纳摩尔浓度的PIA可使异丙肾上腺素和福斯高林对腺苷酸环化酶的刺激作用降低50%。然而，分化几天后，脂肪细胞对NECA的主要阳性反应逐渐丧失，分化10天后对NECA达到稳定反应。PIA对腺苷酸环化酶的抑制作用在分化后至少2周内保持不变。对于从这些细胞获得的细胞膜，NECA和PIA的作用取决于鸟苷三磷酸（GTP）。这些结果表明，在3T3-F442A细胞向脂肪细胞分化的过程中，新的抑制性腺苷受体被表达，而刺激性受体则减弱。
