G alpha(o) is necessary for muscarinic regulation of Ca2+ channels in mouse heart.
Heterotrimeric G proteins, composed of G alpha and G betagamma subunits, transmit signals from cell surface receptors to cellular effector enzymes and ion channels. The G alpha(o) protein is the most abundant G alpha subtype in the nervous system, but it is also found in the heart. Its function is not completely known, although it is required for regulation of N-type Ca2+ channels in GH3 cells and also interacts with GAP43, a major protein in growth cones, suggesting a role in neuronal pathfinding. To analyze the function of G alpha(o), we have generated mice lacking both isoforms of G alpha(o) by homologous recombination. Surprisingly, the nervous system is grossly intact, despite the fact that G alpha(o) makes up 0.2-0.5% of brain particulate protein and 10% of the growth cone membrane. The G alpha(o)-/- mice do suffer tremors and occasional seizures, but there is no obvious histologic abnormality in the nervous system. In contrast, G alpha(o)-/- mice have a clear and specific defect in ion channel regulation in the heart. Normal muscarinic regulation of L-type calcium channels in ventricular myocytes is absent in the mutant mice. The L-type calcium channel responds normally to isoproterenol, but there is no evident muscarinic inhibition. Muscarinic regulation of atrial K+ channels is normal, as is the electrocardiogram. The levels of other G alpha subunits (G alpha(s), G alpha(q), and G alpha(i)) are unchanged in the hearts of G alpha(o)-/- mice, but the amount of G betagamma is decreased. Whichever subunit, G alpha(o) or G betagamma, carries the signal forward, these studies show that muscarinic inhibition of L-type Ca2+ channels requires coupling of the muscarinic receptor to G alpha(o). Other cardiac G alpha subunits cannot substitute.
Valenzuela
D
D
Laboratory of Developmental Biology and Cardiovascular Research Center, Massachusetts General Hospital, Charlestown 02129, USA.
Han
X
X
Mende
U
U
Fankhauser
C
C
Mashimo
H
H
Huang
P
P
Pfeffer
J
J
Neer
E J
EJ
Fishman
M C
MC
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D015139:Blotting, Southern; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002217:Carbachol / Q000494:pharmacology; D002232:Carbocyanines / Q000378:metabolism; D002478:Cells, Cultured; D004562:Electrocardiography; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000235:genetics; D018390:Gene Targeting; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008822:Mice, Transgenic; D009206:Myocardium / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009900:Optic Nerve / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011976:Receptors, Muscarinic / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
C035005:3,3'-dihexadecylindocarbocyanine; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002232:Carbocyanines; D009419:Nerve Tissue Proteins; D011976:Receptors, Muscarinic; D001285:Atropine; D002217:Carbachol; D019204:GTP-Binding Proteins; D007545:Isoproterenol; D000109:Acetylcholine