Comparison of the Ca2+ entry channels responsible for mechanical responses of guinea-pig aorta to noradrenaline and thapsigargin using SK&F 96365 and LOE 908.
Noradrenaline (NA) produces sustained contractions in conduit arteries such as aorta isolated from various animal species. In guinea-pig aorta, NA-produced sustained contraction is largely dependent upon the influx of extracellular Ca2+, but is refractory to the treatment with organic Ca2+ entry blockers. In the present study, we attempted to characterize pharmacologically the Ca2+ entry channel responsible for NA-produced sustained contraction of guinea-pig aorta using SK&F 96365 (1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenylethyl]-1H-imi dazole) and LOE 908 ((R,S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl-N,N-di-[2- (2,3,4-trimethoxyphenyl)ethyl]-acetamide), both of which block voltage-independent Ca2+ channels. The effects of SK&F 96365 and LOE 908 on NA-produced contraction were compared with those on extracellular Ca2+-dependent contractile and endothelium-dependent relaxant responses to thapsigargin (TSG), an inhibitor of Ca2+-pump Ca2+-ATPase. NA (3x10(-6) M)-produced sustained contraction of guinea-pig aorta without endothelium exhibited a strong dependency on the extracellular Ca2+. Nicardipine (10(-7) M), diltiazem (10(-5) M) and verapamil (10(-5) M) did not show any appreciable inhibitory effects on NA-produced sustained contraction. SK&F 96365 concentration-dependently (10(-6)-10(-4) M) attenuated the NA-produced sustained contraction whereas LOE 908 did not affect it at concentrations up to 10(-4) M. Similarly, extracellular Ca2+-dependent contraction of guinea-pig aorta without endothelium in response to TSG was also diminished by SK&F 96365 but was unaffected by LOE 908. In fura-PE3-loaded vascular preparations, SK&F 96365 decreased both cytoplasmic Ca2+ level ([Ca2+]i) and muscle tension elevated by NA and TSG. Both SK&F 96365 and LOE 908 did not affect an endothelium-dependent relaxation of guinea-pig aorta in response to TSG. These findings suggest that in guinea-pig aortic smooth muscle cells, NA activates Ca2+ influx across the plasma-membrane through the Ca2+-permeable channel which is identical with or has similar properties to the store-operated Ca2+ channel (SOCC) stimulated by TSG, but is distinct from endothelial cell SOCC.
Tanaka
Y
Y
Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Funabashi-shi, Chiba, Japan. yotanaka@phar.toho-u.ac.jp
Imai
T
T
Igarashi
T
T
Takayanagi
K
K
Otsuka
K
K
Yamaki
F
F
Tanaka
H
H
Shigenobu
K
K
D000081:Acetamides / Q000494:pharmacology*; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D007093:Imidazoles / Q000494:pharmacology*; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D019284:Thapsigargin / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D000081:Acetamides; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004791:Enzyme Inhibitors; D007093:Imidazoles; D007546:Isoquinolines; C081356:LOE 908; D019284:Thapsigargin; D010738:Type C Phospholipases; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D009638:Norepinephrine