Mechanism of trypsin-induced endothelium-dependent vasorelaxation in the porcine coronary artery

1 To investigate the mechanism underlying the trypsin-induced endothelium-d ependent relaxation, cytosolic Ca2+ concentration ([Ca2+](i)) and tension d evelopment of smooth muscle were simultaneously monitored in the porcine co ronary artery, and [Ca2+](i) of in situ endothelial cells were monitored in the porcine aortic valvular strips, using fura-2 fluorometry. 2 During the contraction induced by 30 nM U46619 a thromboxane A(2) analogu e, 100 nM trypsin induced a rapid transient significant decrease in both [C a2+](i) (from 67.9 +/-5.1 to 15.7 +/-4.4%) and tension (from 97.5 +/-9.2 to 16.8 +/-3.5%) of smooth muscle only in the presence of endothelium (100% l evel was assigned to the level obtained with the 118 mm K+-induced contract ion). [Ca2+], and the tension thus returned to the levels prior to the appl ication of trypsin by 5 and 10 min, respectively. 3 The initial phase of this relaxation was partly inhibited by 100 muM N-om ega-nitro-L-arginine (LNOARG), and was completely inhibited by L-NOARG plus 40 mm K+ or L-NOARG plus 100 nM charybdotoxin and 100 nm apamin, while the late phase of the relaxation was inhibited by L-NOARG alone. 4 Trypsin induced a transient [Ca2+]i elevation in the endothelial cells ma inly due to the Ca2+ release from the intracellular stores, at the concentr ations (1-100 nm) similar to those required to induce relaxation. 5 In conclusion, trypsin induced an elevation in [Ca2+](i) mainly due to Ca 2+ release in endothelial cells, and thereby caused endothelium-dependent r elaxation. The early phase of relaxation was due to nitric oxide and hyperp olarizing factors, while the late phase was mainly due to nitric oxide in t he porcine coronary artery.