The mechanism of the decrease in cytosolic Ca2+ concentrations induced by angiotensin II in the high K(+)-depolarized rabbit femoral artery.
1. Using front-surface fluorometry of fura-2-loaded strips, and measuring the transmembrane 45Ca2+ fluxes of ring preparations of the rabbit femoral artery, the mechanism underlying a sustained decrease in the cytosolic Ca2+ concentration ([Ca2+]i) induced by angiotensin II (AT-II) was investigated. 2. The application of AT-II during steady-state 118 mM K(+)-induced contractions caused a sustained decrease in [Ca2+]i following a rapid and transient increase in [Ca2+]i, while the tension was transiently enhanced. 3. When the intracellular Ca2+ stores were depleted by thapsigargin, the initial rapid and transient increase in [Ca2+]i was abolished, however, neither the sustained decrease in [Ca2+]i nor the enhancement of tension were affected. 4. Depolarization with 118 mM K+ physiological salt solution containing 1.25 mM Ba2+ induced a sustained increase in both the cytosolic Ba2+ concentration ([Ba2+]i) level and tension. However, the application of 10(-6) M AT-II during sustained Ba(2+)-contractions was found to have no effect on [Ba2+]i, but it did enhance tension. 5. After thapsigargin treatment, AT-II neither decreased nor increased the enhanced Ca2+ efflux rate induced by 118 mM K(+)-depolarization, whereas AT-II did increase the enhanced 45Ca2+ influx and the 45Ca2+ net uptake induced by 118 mM K(+)-depolarization. 6. Pretreatment with calphostin-C, partially, but significantly inhibited the decrease in [Ca2+]i induced by AT-II. 7. These findings therefore suggest that AT-II stimulates Ca2+ sequestration into the thapsigargin-insensitive Ca2+ stores, and thus induces a decrease in [Ca2+]i in the high external K(+)-stimulated rabbit femoral artery.
Ushio-Fukai
M
M
Division of Molecular Cardiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Yamamoto
H
H
Nishimura
J
J
Hirano
K
K
Kanaide
H
H
D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005263:Femoral Artery / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009281:Naphthalenes / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011817:Rabbits; D019284:Thapsigargin / Q000494:pharmacology
D002132:Calcium Radioisotopes; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D009281:Naphthalenes; D000804:Angiotensin II; D001464:Barium; D019284:Thapsigargin; D011493:Protein Kinase C; D000252:Calcium-Transporting ATPases; C058819:calphostin C; D011188:Potassium; D002118:Calcium; D016257:Fura-2