Endothelin-1 mediated Ca2+ influx does not occur through L-type voltage-dependent Ca2+ channels in cultured bovine trabecular meshwork cells.
We evaluated whether endothelin-1-induced changes in cytosolic Ca2+ concentration ([Ca2+]i) involve Ca2+ influx through L-type membrane voltage-dependent Ca2+ channels in cultured bovine trabecular meshwork (TM) cells. The cells were loaded with the fluorescent Ca2+ indicator fura-2 and cell-associated fluorescence was measured with a digital video-imaging analyzer. Application of carbachol (10(-3) M) and norepinephrine (10(-5) M) increased [Ca2+]i only transiently. Endothelin-1 (10(-9) M to 10(-7) M) also increased [Ca2+]i in a concentration-dependent manner, and its effects were larger than those of carbachol and norepinephrine. Unlike carbachol or norepinephrine, endothelin-1 evoked a peak transient effect followed by a sustained elevated level of [Ca2+]i. The only level of the sustained elevated component was dependent on extracellular Ca2+. However, pretreatment with diltiazem (10(-5) M and 10(-4) M), an L-type Ca2+ channel blocker, did not affect either component of the endothelin-1-induced increase in [Ca2+]i. These results suggest that in cultured bovine TM cells endothelin-1 receptors are coupled to Ca2+ signaling mechanisms. However, the extracellular Ca(2+)-dependent increase in [Ca2+]i may not involve Ca2+ influx through L-type Ca2+ channels.
Kageyama
M
M
Ophthalmic Research Division, Santen Pharmaceutical Co., Ltd., Osaka, Japan.
Fujita
M
M
Shirasawa
E
E
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D004110:Diltiazem / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D019332:Endothelin-1 / Q000494:pharmacology*; D005456:Fluorescent Dyes; D016257:Fura-2; D018721:Muscarinic Agonists / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D017466:Receptors, Endothelin / Q000378:metabolism; D015398:Signal Transduction; D014129:Trabecular Meshwork / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D000316:Adrenergic alpha-Agonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D019332:Endothelin-1; D005456:Fluorescent Dyes; D018721:Muscarinic Agonists; D017466:Receptors, Endothelin; D002217:Carbachol; D004110:Diltiazem; D002118:Calcium; D016257:Fura-2; D009638:Norepinephrine