Role of G proteins in agonist-induced Ca2+ sensitization of tracheal smooth muscle.
Increased sensitivity to intracellular Ca2+ concentration ([Ca2+]) is an important mechanism for agonist-induced contraction of airway smooth muscle, but the signal transduction pathways involved are uncertain. We studied Ca2+ sensitization with acetylcholine (ACh) and endothelin (ET)-1 in porcine tracheal smooth muscle by measuring contractions at a constant [Ca2+] in strips permeabilized with alpha-toxin or beta-escin. The peptide inhibitor G protein antagonist 2A (GP Ant-2A), which has selectivity for Gq over Gi, inhibited contractile responses to ET-1, ACh, and guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS), but the proportional inhibition of ACh responses was less than that of ET-1. Pretreatment with pertussis toxin reduced ACh contractions but had no effect on those of ET-1 or GTPgammaS. Clostridium botulinum C3 exoenzyme, which inactivates Rho family monomeric G proteins, caused similar reductions in contractile responses to ACh, ET-1, and GTPgammaS. Farnesyltransferase inhibition, which inhibits Ras G proteins, reduced responses to ET-1. We conclude that the heterotrimeric G proteins Gq and Gi both contribute to Ca2+ sensitization by ACh, whereas ET-1 responses involve Gq but not Gi. Both Gq and Gi pathways likely involve Rho family small G proteins. A Ras-mediated pathway also contributes to Ca2+ sensitization by ET-1 in airway smooth muscle.
Departments of Environmental Health Sciences and Anesthesiology and Critical Care Medicine, The Johns Hopkins Medical Institutions, Baltimore, Maryland 21205, USA.
T L
TL
Croxton
B
B
Lande
C A
CA
Hirshman
D036002:ADP Ribose Transferases / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001905:Botulinum Toxins; D002118:Calcium / Q000378:metabolism*; D019332:Endothelin-1 / Q000494:pharmacology; D004928:Escin / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D046911:Macromolecular Substances; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D037342:Pertussis Toxin; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013552:Swine; D014132:Trachea / Q000187:drug effects / Q000502:physiology*; D010738:Type C Phospholipases / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D019332:Endothelin-1; D046911:Macromolecular Substances; D010566:Virulence Factors, Bordetella; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004928:Escin; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000109:Acetylcholine; D002118:Calcium