期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2020
卷号：117
期号：25
页码：14522-14531
DOI：10.1073/pnas.2001270117
出版社：The National Academy of Sciences of the United States of America
摘要：How G protein-coupled receptors (GPCRs) evoke specific biological outcomes while utilizing a limited array of G proteins and effectors is poorly understood, particularly in native cell systems. Here, we examined signaling evoked by muscarinic (M 2 R) and adenosine (A 1 R) receptor activation in the mouse sinoatrial node (SAN), the cardiac pacemaker. M 2 R and A 1 R activate a shared pool of cardiac G protein-gated inwardly rectifying K (GIRK) channels in SAN cells from adult mice, but A 1 R-GIRK responses are smaller and slower than M 2 R-GIRK responses. Recordings from mice lacking Regulator of G protein Signaling 6 (RGS6) revealed that RGS6 exerts a GPCR-dependent influence on GIRK-dependent signaling in SAN cells, suppressing M 2 R-GIRK coupling efficiency and kinetics and A 1 R-GIRK signaling amplitude. Fast kinetic bioluminescence resonance energy transfer assays in transfected HEK cells showed that RGS6 prefers Gα o over Gα i as a substrate for its catalytic activity and that M 2 R signals preferentially via Gα o , while A 1 R does not discriminate between inhibitory G protein isoforms. The impact of atrial/SAN-selective ablation of Gα o or Gα i2 was consistent with these findings. Gα i2 ablation had minimal impact on M 2 R-GIRK and A 1 R-GIRK signaling in SAN cells. In contrast, Gα o ablation decreased the amplitude and slowed the kinetics of M 2 R-GIRK responses, while enhancing the sensitivity and prolonging the deactivation rate of A 1 R-GIRK signaling. Collectively, our data show that differences in GPCR-G protein coupling preferences, and the Gα o substrate preference of RGS6, shape A 1 R- and M 2 R-GIRK signaling dynamics in mouse SAN cells.
关键词：muscarinic ; adenosine ; Kir3 ; G protein ; heart rate
