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

To investigate the mechanism underlying the trypsin-induced endothelium-dependent relaxation, cytosolic Ca2+ concentration ([Ca2+]i) and tension development of smooth muscle were simultaneously monitored in the porcine coronary artery, and [Ca2+]i of in situ endothelial cells were monitored in the porcine aortic valvular strips, using fura-2 fluorometry. During the contraction induced by 30 nM U46619, a thromboxane A2 analogue, 100 nM trypsin induced a rapid transient significant decrease in both [Ca2+]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% level was assigned to the level obtained with the 118 mM K+-induced contraction). [Ca2+]i and the tension thus returned to the levels prior to the application of trypsin by 5 and 10 min, respectively. The initial phase of this relaxation was partly inhibited by 100 μM Nω-nitro-L-arginine (L-NOARG), 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. Trypsin induced a transient [Ca2+]i elevation in the endothelial cells mainly due to the Ca2+ release from the intracellular stores, at the concentrations (1 – 100 nM) similar to those required to induce relaxation. In conclusion, trypsin induced an elevation in [Ca2+]i mainly due to Ca2+ release in endothelial cells, and thereby caused endothelium-dependent relaxation. The early phase of relaxation was due to nitric oxide and hyperpolarizing factors, while the late phase was mainly due to nitric oxide in the porcine coronary artery. British Journal of Pharmacology (2001) 134, 815–826; doi:10.1038/sj.bjp.0704318