Vortherms Timothy A, Nguyen Chau H, Bastepe Murat, Jüppner Harald, Watts Val J
Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, 575 Stadium Mall Dr., RHPH 210 West Lafayette, IN 47907, USA.
Neuropharmacology. 2006 Apr;50(5):576-84. doi: 10.1016/j.neuropharm.2005.11.004. Epub 2005 Dec 27.
Acute activation of D2 dopamine receptors inhibits adenylyl cyclase (EC 4.6.1.1), whereas persistent activation of these inhibitory receptors results in a compensatory increase in cyclic AMP accumulation. This sensitization of adenylyl cyclase is thought to involve enhanced Galpha(s)-adenylyl cyclase interactions; however, the absolute requirement of Galpha(s) has not been determined. The present study used a Galpha(s)-deficient cell line to examine directly the role of Galpha(s) in D2 dopamine receptor-induced sensitization of recombinant adenylyl cyclase type 1 (AC1) and 5 (AC5). In acute experiments, quinpirole activation of the D2 dopamine receptor inhibited AC1 and AC5 activity, indicating that the acute regulatory properties of AC1 and AC5 were retained in the absence of Galpha(s). Subsequent experiments revealed that short-term (2 h) activation of the D2 dopamine receptor resulted in significantly enhanced forskolin-stimulated AC1 activity in the absence of Galpha(s), whereas sensitization of forskolin-stimulated AC5 activity appeared to require Galpha(s). The Galpha(s)-independent sensitization of AC1 was explored further using AC1-selective activation protocols (A23187 and CCE) following short- and long-term agonist treatment. These studies revealed that persistent activation of D2 dopamine receptors sensitized AC1 activity to Ca2+ stimulation in cells devoid of endogenous Galpha(s) and demonstrate directly that sensitization of AC1 is Galpha(s)-independent.
D2多巴胺受体的急性激活会抑制腺苷酸环化酶（EC 4.6.1.1），而这些抑制性受体的持续激活会导致环磷酸腺苷积累的代偿性增加。腺苷酸环化酶的这种敏化作用被认为涉及增强的Gα(s)-腺苷酸环化酶相互作用；然而，Gα(s)的绝对需求尚未确定。本研究使用了一种缺乏Gα(s)的细胞系，以直接研究Gα(s)在D2多巴胺受体诱导的重组1型腺苷酸环化酶（AC1）和5型腺苷酸环化酶（AC5）敏化中的作用。在急性实验中，喹吡罗激活D2多巴胺受体抑制了AC1和AC5的活性，表明在缺乏Gα(s)的情况下，AC1和AC5的急性调节特性得以保留。随后的实验表明，在缺乏Gα(s)的情况下，D2多巴胺受体的短期（2小时）激活导致福斯高林刺激的AC1活性显著增强，而福斯高林刺激的AC5活性的敏化似乎需要Gα(s)。在短期和长期激动剂处理后，使用AC1选择性激活方案（A23187和CCE）进一步探讨了AC1的不依赖Gα(s)的敏化作用。这些研究表明，D2多巴胺受体的持续激活使缺乏内源性Gα(s)的细胞中的AC1活性对Ca2+刺激敏感，并直接证明AC1的敏化是不依赖Gα(s)的。
