Calcium mobilization induced by endothelins and sarafotoxin in cultured canine tracheal smooth muscle cells.
Endothelins (ETs)- and sarafotoxin (S6b)-induced rises in intracellular Ca2+ concentration ([Ca2+]i) were monitored in cultured canine tracheal smooth muscle cells by using a fluorescent Ca2+ indicator fura-2. ET-1, ET-2, ET-3 and S6b elicited an initial transient peak and followed by a sustained elevation of [Ca2+]i, with half-maximal effect (EC50) of 18, 20, 38 and 21 nM, respectively. BQ-123, an ETA receptor antagonist, had a high affinity to block the rise in [Ca2+]i response to ET-1, ET-2, and S6b, as well as a low affinity for ET-3. Removal of external Ca2+ by addition of EGTA during the sustained phase, caused a rapid decline in [Ca2+]i to the resting level. In the absence of external Ca2+, only an initial transient peak of [Ca2+]i was seen, the sustained elevation of [Ca2+]i could then be evoked by addition of 1.8 mM Ca2+. Ca2+ influx was required for the changes of [Ca2+]i, since the Ca(2+)-channel blockers, diltiazem, verapamil, and Ni2+, decreased both the initial and sustained elevation of [Ca2+]i response to these peptides. ETs exhibited homologous desensitization of the Ca2+ response, but partial heterologous desensitization of the Ca2+ response mediated by carbachol to different extents. In contrast, ETs did not desensitize the Ca2+ response induced by ATP or vice versa. These data demonstrate that the initial detectable increase in [Ca2+]i stimulated by these peptides is due to the activation of ETA receptors and subsequently the release of Ca2+ from internal stores, whereas the contribution of external Ca2+ follows and partially involves a diltiazem- and verapamil-sensitive process.(ABSTRACT TRUNCATED AT 250 WORDS)
Yang
C M
CM
Department of Pharmacology, Chang Gung Medical College, Tao-Yuan, Taiwan, Republic of China.
Yo
Y L
YL
Ong
R
R
Hsieh
J T
JT
Tsao
H L
HL
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D004110:Diltiazem / Q000494:pharmacology; D004285:Dogs; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000494:pharmacology*; D005260:Female; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014700:Verapamil / Q000494:pharmacology; D014757:Viper Venoms / Q000494:pharmacology*
D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D010456:Peptides, Cyclic; D014662:Vasoconstrictor Agents; D014757:Viper Venoms; C057354:sarafotoxins s6; D002217:Carbachol; D014700:Verapamil; D004110:Diltiazem; C072247:cyclo(Trp-Asp-Pro-Val-Leu); D002118:Calcium