Amlodipine activates the endothelial nitric oxide synthase by altering phosphorylation on Ser1177 and Thr495.
OBJECTIVE
The Ca2+ antagonist amlodipine increases the generation of nitric oxide (NO) from native and cultured endothelial cells. The aim of this investigation was to determine whether or not the activation of the endothelial NO synthase (eNOS) by this Ca2+ antagonist is related to alterations in eNOS phosphorylation.


RESULTS
In isolated, pre-contracted, endothelium-intact porcine coronary arteries, amlodipine elicited an NO-mediated relaxation and a leftward shift in the concentration-relaxation curve to bradykinin. Moreover, the Ca2+ antagonist increased the generation of NO from native endothelial cells, as detected by electron spin resonance spectroscopy and stimulated an 8-fold increase in cyclic GMP levels in cultured endothelial cells. In unstimulated endothelial cells, eNOS was not phosphorylated on Ser1177 but was phosphorylated on Thr495. Amlodipine elicited the phosphorylation of Ser1177 and attenuated Thr495 phosphorylation, with a time course similar to that of eNOS activation. The amlodipine-induced relaxation of porcine coronary arteries was attenuated by the B2 kinin receptor antagonist, icatibant, but this antagonist did not affect amlodipine-induced changes in eNOS phosphorylation in cultured endothelial cells. Moreover, amlodipine elicited the NO-mediated relaxation of rat aortic rings which do not express the B2 receptor. Amlodipine time-dependently attenuated the phosphorylation of protein kinase C (PKC) in endothelial cells, with a time course similar to the changes in eNOS phosphorylation, and prevented the phorbol-12-myristate-13-acetate-induced activation of PKC. The PKC inhibitor, Ro 31-8220, also elicited the phosphorylation of Ser1177 and the dephosphorylation of Thr495 in cultured cells and induced a leftward shift in the concentration-relaxation curve to bradykinin in rings of porcine coronary artery.


CONCLUSIONS
The Ca2+ antagonist, amlodipine, enhances endothelial NO generation by inducing changes in the phosphorylation of eNOS. Although the activation of eNOS was related to the activation of the B2 kinin receptor in the porcine coronary artery, a B2 receptor-independent mechanism involving the inhibition of PKC appears to account for the effects observed in the rat aorta as well as in cultured endothelial cells.
Lenasi
Helena
H
Institut für Kardiovaskuläre Physiologie, Klinikum der JWG-Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany.
Kohlstedt
Karin
K
Fichtlscherer
Birgit
B
Mülsch
Alexander
A
Busse
Rudi
R
Fleming
Ingrid
I
D017311:Amlodipine / Q000494:pharmacology*; D000818:Animals; D001011:Aorta; D001920:Bradykinin / Q000031:analogs & derivatives* / Q000494:pharmacology; D065094:Bradykinin B2 Receptor Antagonists; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002478:Cells, Cultured; D003331:Coronary Vessels; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D011921:Rats, Inbred WKY; D012694:Serine / Q000378:metabolism; D013552:Swine; D013912:Threonine / Q000378:metabolism; D014471:Umbilical Veins; D014664:Vasodilation / Q000187:drug effects
D065094:Bradykinin B2 Receptor Antagonists; D002121:Calcium Channel Blockers; D007211:Indoles; D017311:Amlodipine; D013912:Threonine; D009569:Nitric Oxide; D012694:Serine; C065679:icatibant; D019001:Nitric Oxide Synthase; D011493:Protein Kinase C; D001920:Bradykinin; C064758:Ro 31-8220