Role of endothelium in thapsigargin-induced arterial responses in rat aorta.
We assessed the role of endothelium in the arterial response to thapsigargin, the Ca(2+)-ATPase inhibitor of the endoplasmic reticulum, in rat isolated aortic rings. Thapsigargin induced an endothelium-dependent relaxation of phenylephrine-contracted aortic rings with an EC(50) of 2.6+/-0.4 nM and a 75% maximum relaxation, while it was less effective against 30 mM K(+)-induced contraction. Pretreatment of aortic rings with N(G)-nitro-L-arginine methyl ester (30 microM) or methylene blue (1 microM) reduced thapsigargin-induced relaxation by approximately 85%. Thapsigargin failed to relax the endothelium-denuded rings. L-Arginine (3 mM) partially, but significantly, antagonized the effect of 30 microM N(G)-nitro-L-arginine methyl ester. Pretreatment with indomethacin (3 microM), glibenclamide (1 microM) or iberiotoxin (100 nM) did not alter the thapsigargin-induced relaxation. In contrast, pretreatment with tetrapentylammonium ions (TPA(+), 1-3 microM) or with 300 microM Ba(2+) suppressed the relaxant response to thapsigargin. TPA(+) (3 microM) also attenuated acetylcholine-induced relaxation. Thapsigargin-induced endothelium-dependent relaxation was primarily dependent on the presence of extracellular Ca(2+). Interestingly, when the tissues were exposed to very low concentrations of thapsigargin (1-3 nM) the nitric oxide-dependent relaxation induced by acetylcholine or A23187 was markedly reduced. While thapsigargin (3 nM) did not influence the relaxation induced by endothelium-independent dilators, sodium nitroprusside and verapamil. These results indicate that thapsigargin produced complex vascular effects primarily by acting on the endothelial cells. Thapsigargin causes an endothelial nitric oxide-dependent relaxation; on the other hand, it inhibits nitric oxide-mediated relaxation at the similar concentrations. Activation of TPA(+)- and Ba(2+)-sensitive but not Ca(2+)-activated or ATP-sensitive K(+) channels may be also involved in thapsigargin-induced relaxation of rat isolated aortic rings.
Huang
Y
Y
Department of Physiology, Faculty of Medicine, Chinese University of Hong Kong, Shatin, Hong Kong, People's Republic of China. yu-huang@cuhk.edu.hk
Yao
X
X
Lau
C
C
Chan
F L
FL
Chan
N W
NW
Cheng
Y
Y
Chen
Z
Z
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000502:physiology*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000502:physiology; D019335:Nitroarginine / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects
D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D019335:Nitroarginine; D009569:Nitric Oxide; D000001:Calcimycin; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium; D019331:NG-Nitroarginine Methyl Ester