Ca2+ entry channels in rat thoracic aortic smooth muscle cells activated by endothelin-1.
The contraction of the rat aorta induced by endothelin-1 (ET-1) requires entry of extracellular Ca2+, but involvement of voltage-operated Ca2+ channel is minor. Using whole-cell recordings of patch-clamp and monitoring of the intracellular free Ca2+ concentration ([Ca2+]i), we characterized Ca2+ entry channels in A7r5 cells activated by ET-1. ET-1 activates three types of voltage-independent Ca2+ entry channels: two types of Ca2+-permeable nonselective cation channels (designated NSCC-1 and NSCC-2) and a store-operated Ca2+ channel (SOCC). Furthermore, it was found that these channels can be pharmacologically discriminated using Ca2+ channel blockers such as SK&F 96365 and LOE 908. NSCC-1 is resistant to SK&F 96365, but sensitive to LOE 908, whereas NSCC-2 is sensitive to both SK&F 96365 and LOE 908. SOCC is sensitive to SK&F 96365, but resistant to LOE 908. Using these channel blockers, we analyzed Ca2+ entry channels involved in the ET-1-induced contractions of rat thoracic aorta and increases in [Ca2+]i of single smooth muscle cells. The responses to lower concentrations of ET-1 (< or = 0.1 nM) were abolished by either SK&F 96365 or LOE 908 alone. In contrast, the responses to higher concentrations of ET-1 (> or = 1 nM) were suppressed by SK&F 96365 or LOE 908 to about 10% and 35% of controls, respectively, and abolished by combined treatment with SK&F 96365 and LOE 908. These results show that the responses of rat aorta to lower concentrations of ET-1 involve only one Ca2+ channel that is sensitive to SK&F 96365 and LOE 908 (NSCC-2), whereas those to higher concentrations of ET-1 involve NSCC-1, NSCC-2 and SOCC, contributing 10%, 55% and 35%, respectively, to total Ca2+ entry.
Miwa
S
S
Department of Pharmacology, Kyoto University Faculty of Medicine, Japan.
Iwamuro
Y
Y
Zhang
X F
XF
Inoki
T
T
Okamoto
Y
Y
Okazawa
M
M
Masaki
T
T
D000081:Acetamides / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology; D019332:Endothelin-1 / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D051381:Rats
D000081:Acetamides; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D019332:Endothelin-1; D007093:Imidazoles; D007546:Isoquinolines; C081356:LOE 908; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole