Functional expression of the GABAB receptor in human airway smooth muscle.
gamma-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian central nervous system and exerts its actions via both ionotropic (GABA(A)/GABA(C)) and metabotropic (GABA(B)) receptors (R). In addition to their location on neurons, GABA and functional GABA(B) receptors have been detected in nonneuronal cells in peripheral tissue. Although the GABA(B)R has been shown to function as a prejunctional inhibitory receptor on parasympathetic nerves in the lung, the expression and functional coupling of GABA(B) receptors to G(i) in airway smooth muscle itself have never been described. We detected the mRNA encoding multiple-splice variants of the GABA(B)R1 and GABA(B)R2 in total RNA isolated from native human and guinea pig airway smooth muscle and from RNA isolated from cultured human airway smooth muscle (HASM) cells. Immunoblots identified the GABA(B)R1 and GABA(B)R2 proteins in human native and cultured airway smooth muscle. The GABA(B)R1 protein was immunohistochemically localized to airway smooth muscle in guinea pig tracheal rings. Baclofen, a GABA(B)R agonist, elicited a concentration-dependent stimulation of [(35)S]GTPgammaS binding in HASM homogenates that was abrogated by the GABA(B)R antagonist CGP-35348. Baclofen also inhibited adenylyl cyclase activity and induced ERK phosphorylation in HASM. Another GABA(B)R agonist, SKF-97541, mimicked while pertussis toxin blocked baclofen's effect on ERK phosphorylation, implicating G(i) protein coupling. Functional GABA(B) receptors are expressed in HASM. GABA may modulate an uncharacterized signaling cascade via GABA(B) receptors coupled to the G(i) protein in airway smooth muscle.
Osawa
Yoko
Y
Department of Anesthesiology, College of Physicians and Surgeons of Columbia University, 630 W. 168th St., P&S Box 46, New York, NY 10032, USA.
Xu
Dingbang
D
Sternberg
David
D
Sonett
Joshua R
JR
D'Armiento
Jeanine
J
Panettieri
Reynold A
RA
Emala
Charles W
CW
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006168:Guinea Pigs; D006801:Humans; D007150:Immunohistochemistry; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology*; D018080:Receptors, GABA-B / Q000235:genetics* / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology; D013462:Sulfur Radioisotopes; D014132:Trachea / Q000166:cytology / Q000502:physiology*
C485503:GABBR2 protein, human; D018080:Receptors, GABA-B; D013462:Sulfur Radioisotopes; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D048049:Extracellular Signal-Regulated MAP Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases