ETA and ETB receptors on single smooth muscle cells cooperate in mediating guinea pig tracheal contraction.
We investigated the distribution of endothelin A (ETA) and ETB receptors in single smooth muscle cells and their contribution to ET-induced contractions of guinea pig trachea. ETA and ETB receptors were detected in smooth muscle membranes (maximum binding capacities of 810 and 360 fmol/mg protein and dissociation constants of 38 and 5.1 pM for 125I-labeled ET-1 and 125I-ET-3, respectively) and visualized autoradiographically in primary cultured cells. ET-1 and ET-3 evoked concentration-dependent increases in intracellular Ca2+ concentration and smooth muscle tension. The half-maximally effective concentrations of ET-1 and ET-3 at inducing contractions were 1.9 and 2.7 nM, respectively. The Ca2+ responses showed tachyphylaxis to both ETs after stimulation with ET-1, but only to ET-3 after stimulation with ET-3. Consecutive applications of ET-3 and ET-1 (10 nM each) classified the cells into ETA dominant (approximately 30%) responding to only ET-1, ETB dominant (approximately 20%) responding to only ET-3, and ETA- and ETB-possessing (approximately 50%) cells responding to both. The ETA antagonist, 10 microM BQ-123, attenuated ET-1-induced contractions but did not affect the ET-3-induced contractions. The results indicate that both receptors coexist in a major population of smooth muscle cells and cooperate in mediating ET-1-induced contractions.
Inui
T
T
International Research Laboratories, Ciba-Geigy Japan, Takarazuka.
James
A F
AF
Fujitani
Y
Y
Takimoto
M
M
Okada
T
T
Yamamura
T
T
Urade
Y
Y
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D016232:Endothelins / Q000494:pharmacology; D016257:Fura-2; D006168:Guinea Pigs; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism* / Q000502:physiology*; D009994:Osmolar Concentration; D017466:Receptors, Endothelin / Q000378:metabolism*; D014132:Trachea / Q000166:cytology / Q000378:metabolism* / Q000502:physiology*
D016232:Endothelins; D017466:Receptors, Endothelin; D002118:Calcium; D016257:Fura-2