PT - JOURNAL ARTICLE AU - Simen, Arthur A. AU - Miller, Richard J. TI - Involvement of Regions in Domain I in the Opioid Receptor Sensitivity of α1B Ca<sup>2+</sup> Channels DP - 2000 May 01 TA - Molecular Pharmacology PG - 1064--1074 VI - 57 IP - 5 4099 - http://molpharm.aspetjournals.org/content/57/5/1064.short 4100 - http://molpharm.aspetjournals.org/content/57/5/1064.full SO - Mol Pharmacol2000 May 01; 57 AB - The structural basis of Ca2+ channel inhibition by G proteins has received considerable attention recently, and multiple regions on Ca2+ channels that interact with G protein subunits have been identified. We have demonstrated previously that a region extending from the N terminus to the I/II loop of the Ca2+ channel is involved in determining the differences between α1B and α1E Ca2+ channels with respect to inhibition by G proteins. Here we explore this region of the channel in greater detail in an effort to further define the regions involved in determining inhibition. Chimeric Ca2+ channels constructed from α1B and α1E Ca2+ channels revealed that the N terminus, the I/II loop, and domain I all play an important role in determining inhibition. We identified a 70-amino acid fragment from domain I that mediates the effects of domain I, and a 50-amino acid fragment from the I/II loop that mediates the effects of the I/II loop. When these regions from α1B were exchanged into α1E, inhibition identical with that of α1B was observed. The differences between α1B and α1E in the identified region of domain I involve residues that are predicted to be almost exclusively extracellular. Mutations to some of the high-affinity G protein binding regions of α1B (α interaction domain, CC14, and a C-terminal Gα binding site) caused relatively little change in inhibition, which suggests that these sites are not necessary individually for G protein-mediated inhibition and may help to explain the small effects of exchanging these regions in isolation. The American Society for Pharmacology and Experimental Therapeutics