Fenton Richard A, Dobson James G
Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
J Cell Physiol. 2007 Dec;213(3):785-92. doi: 10.1002/jcp.21149.
In the heart beta1-adrenergic (beta1R) and adenosine A1 (A1R) and A2A (A2AR) receptors modulate contractile and metabolic function. The interaction between these receptors was investigated at the level of G-protein cycling by determining the effect of receptor agonists on the binding of GTP to G-proteins and displacement of G alpha-subunit-bound GDP by GTP. Crude membranes from rat heart or brain were stimulated by agonists for beta1R (isoproterenol; ISO), A1R (chlorocyclopentyladenosine, CCPA) and A2AR (CGS-21680; CGS). GTP binding to membranes was increased by ISO (17%), CCPA (6%) and CGS (12%). Binding values observed with incubation using ISO and CCPA together were significantly less than values obtained by the incubation of individual agents alone. With ISO, GTP binding to G alpha(s) subunits as determined by immunoprecipitation was increased 79% in heart and 87% in brain. These increases were attenuated by CCPA, an effect that was inhibited by CGS. GDP release by membranes was increased 6.9% and 4.6% by ISO and CCPA, respectively. After co-incubation of these agonists, release was increased less than determined by the addition of the individual agent responses. CGS inhibited the reduced release caused by of CCPA. Adenylyl cyclase activity stimulated by ISO was attenuated 33% by CCPA, an effect inhibited by CGS. Together, these results indicate that A1R exert an antiadrenergic action at the level of beta1R stimulated G(s)-protein cycling and that A2AR reduce this action.
在心脏中，β1 - 肾上腺素能（β1R）、腺苷A1（A1R）和A2A（A2AR）受体调节收缩和代谢功能。通过测定受体激动剂对GTP与G蛋白结合以及GTP置换Gα亚基结合的GDP的影响，在G蛋白循环水平上研究了这些受体之间的相互作用。用β1R激动剂（异丙肾上腺素；ISO）、A1R激动剂（氯环戊基腺苷，CCPA）和A2AR激动剂（CGS - 21680；CGS）刺激大鼠心脏或大脑的粗制膜。ISO（17%）、CCPA（6%）和CGS（12%）可增加GTP与膜的结合。同时使用ISO和CCPA孵育时观察到的结合值显著低于单独使用各试剂孵育获得的值。对于ISO，通过免疫沉淀测定，心脏中与Gα(s)亚基结合的GTP增加79%，大脑中增加87%。这些增加被CCPA减弱，而CGS可抑制这种作用。膜释放GDP分别被ISO和CCPA增加6.9%和4.6%。这些激动剂共同孵育后，释放增加量小于单独添加各试剂时的反应之和。CGS抑制了CCPA引起的释放减少。ISO刺激的腺苷酸环化酶活性被CCPA减弱33%，CGS可抑制这种作用。总之，这些结果表明A1R在β1R刺激的G(s)蛋白循环水平上发挥抗肾上腺素能作用，而A2AR可减弱这种作用。
