The stimulatory G protein of adenylyl cyclase, Gs, also stimulates dihydropyridine-sensitive Ca2+ channels. Evidence for direct regulation independent of phosphorylation by cAMP-dependent protein kinase or stimulation by a dihydropyridine agonist.
We demonstrated recently that purified preparations of Gs, the stimulatory G protein of adenylyl cyclase, can stabilize Ca2+ channels in inside-out cardiac ventricle membrane patches stimulated prior to excision by the beta-adrenergic agonist isoprenaline or by the dihydropyridine agonist Bay K 8644 and that such preparations of Gs can restore activity to spontaneously inactivated cardiac Ca2+ channels incorporated into planar lipid bilayers (Yatani, A., Codina, J., Reeves, J.P., Birnbaumer, L., and Brown, A.M. (1987) Science 238, 1288-1292). To test whether these effects represented true stimulation and to further identify the G protein responsible, we incorporated skeletal muscle T-tubule membranes into lipid bilayers and studied the response of their Ca2+ channels to G proteins, specifically Gs, and manipulations known to be specific for Gs. In contrast to cardiac channels, incorporated T-tubule Ca2+ channels exhibit stable average activities over prolonged periods of time (up to 20 min at room temperature), allowing assessment of possible effects of G proteins under steady-state assay conditions. We report that exogenously added human erythrocyte GTP gamma S (guanosine 5'-O-(3-thiotriphosphate]-activated Gs (Gs) or its resolved GTP gamma S-activated alpha subunit (alpha s) stimulate T-tubule Ca2+ channels by factors of 2-3 in the presence of Bay K 8644, and of 10-20 in the absence of Bay K 8644 and that they do so in a manner that is independent of concurrent or previous phosphorylation by cAMP-dependent protein kinase. Activation of purified Gs by cholera toxin increases both its adenylyl cyclase stimulatory and its Ca2+ channel stimulatory effects. Ca2+ channels previously stimulated by the combined actions of Bay K 8644 and cAMP-dependent protein kinase still respond to Gs. We conclude that the responses seen are due to Gs rather than a contaminant, that the effect on Ca2+ channel activity is that of a true stimulation, akin to that on adenylyl cyclase, and show that a given G protein may regulate more than one effector system.
Yatani
A
A
Department of Physiology, Baylor College of Medicine, Houston, Texas 77030.
Imoto
Y
Y
Codina
J
J
Hamilton
S L
SL
Brown
A M
AM
Birnbaumer
L
L
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004095:Dihydropyridines / Q000494:pharmacology*; D004553:Electric Conductivity; D004912:Erythrocytes / Q000032:analysis; D019204:GTP-Binding Proteins / Q000494:pharmacology*; D006150:Guanine Nucleotides / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008051:Lipid Bilayers / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D013873:Thionucleotides / Q000494:pharmacology
D004095:Dihydropyridines; D006150:Guanine Nucleotides; D007473:Ion Channels; D008051:Lipid Bilayers; D013873:Thionucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D006160:Guanosine Triphosphate; D002772:Cholera Toxin; D000242:Cyclic AMP; D011494:Protein Kinases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D002118:Calcium