title: A substantial proportion of cardiac Gs is not associated with the plasma membrane.
abstract: The precise interactions between the subunits of Gs (alpha s, beta, gamma) and the plasma membrane remain to be established. If alpha s is associated loosely with the inner membrane, is labile during activation, or is always present to some extent in the cytoplasm, then it should fractionate to the supernatant of a high-speed centrifugation. We identified abundant alpha s (52-66% of total cellular) in the supernatant fraction of right atrial and left ventricular membrane preparations of porcine heart as shown by two distinct measures of alpha s (immunoblotting and ADP ribosylation by cholera toxin). However, functional assays utilizing reconstitution of cardiac alpha s with cyc- S49 membranes revealed that the supernatant fraction contained approximately 16% of total cellular alpha s activity. The alpha s present in the supernatant fraction did not result from contamination by sarcolemmal membrane fragments. We conclude that traditional methods for quantifying alpha s which utilize only detergent extracts from high-speed pellets do not account for a sizable proportion of total cellular alpha s, but that the majority of this population of cardiac alpha s may not be functional, at least with respect to adenylyl cyclase activation.
authors.affiliation: VAMC-San Diego, CA 92161.
authors.forename: D A
authors.initials: DA
authors.lastname: Roth
authors.forename: K
authors.initials: K
authors.lastname: Urasawa
authors.forename: D
authors.initials: D
authors.lastname: Leiber
authors.forename: P A
authors.initials: PA
authors.lastname: Insel
authors.forename: H K
authors.initials: HK
authors.lastname: Hammond
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D002772:Cholera Toxin / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D015398:Signal Transduction; D013552:Swine
chemical_list: D008565:Membrane Proteins; D000246:Adenosine Diphosphate Ribose; D002772:Cholera Toxin; D019204:GTP-Binding Proteins