Selective activation of excitation-contraction coupling pathways by ET(A) and ET(B) receptors in guinea-pig tracheal smooth muscle.
1. Signalling events responsible for endothelin(A) (ET(A)) and ET(B) receptor-induced contraction were examined in epithelium-denuded guinea-pig tracheal smooth muscle strips. Selective stimulation of each subtype was achieved by a combination of ET-1 (100 nM) and ET(A) and ET(B) receptor-selective antagonists, BQ-123 (10 microM) and BQ-788 (3 microM), respectively. 2. Both ET(A) and ET(B) receptors induced long-lasting contraction that was totally dependent on Ca2+ influx. Stimulation of ET(A) receptor induced both transient and sustained (Ca2+)i increases whereas that of ET(B) receptor induced only a sustained increase. Suppression of the transient (Ca2+)i increase by U73122 (3 microM) did not affect the ET(A)-induced sustained (Ca2+)i increase and tension development. Stimulation of ET(A) receptor, but not ET(B), induced phosphoinositide breakdown and protein kinase C (PKC). The activated PKC contributed to the contraction by increasing the Ca2+ sensitivity of the contractile apparatus. 3. Thus, ET(A) receptor is coupled both with phospholipase C/Ca2+/PKC signalling and Ca2+ influx pathways whereas ET(B) receptor was coupled only with the latter. 4. Stimulation of ET(B) receptor, but not ET(A), caused membrane depolarization measured with a fluorescent indicator, bis-(1,3 dibutylbarbituric acid)-trimethine oxonol. Both nifedipine (1 microM) and verapamil (10 microM) abolished ET(B)-induced Ca2+ influx and contraction, while they barely affected ET(A)-induced responses. 5. Therefore, the Ca2+ influx pathways activated by each subtype appeared to be completely different; ET(A) and ET(B) receptors opens voltage-independent Ca2+ channels and L-type voltage-dependent Ca2+ channels, respectively.
Inui
T
T
International Research Laboratories, Ciba-Geigy Japan, Takarazuka.
Ninomiya
H
H
Sasaki
Y
Y
Makatani
M
M
Urade
Y
Y
Masaki
T
T
Yamamura
T
T
D000818:Animals; D002118:Calcium / Q000378:metabolism; D019332:Endothelin-1 / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology*; D011493:Protein Kinase C / Q000502:physiology; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000502:physiology*; D014132:Trachea / Q000502:physiology*; D010738:Type C Phospholipases / Q000502:physiology
D019332:Endothelin-1; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; D011493:Protein Kinase C; D010738:Type C Phospholipases; D002118:Calcium