Ca2+ influx in the endothelial cells is required for the bradykinin-induced endothelium-dependent contraction in the porcine interlobar renal artery

1. To determine the mechanists of bradykinin-induced production of endothel ium-derived contracting factors, we monitored the changes in cytosolic Ca2 concentration ([Ca2+](i)) in situ endothelial cells in porcine aortic valv ular strips and the changes in [Ca2+](i) of smooth muscle cells and force i n porcine interlobar renal arterial strips using front-surface fluorometry of fura-2. 2. In the presence of N-omega-nitro-L-arginine methyl ester, bradykinin cau sed an endothelium-dependent transient elevation of [Ca2+](i) and contracti on in smooth muscle in the interlobar renal artery. This contraction was co mpletely inhibited by a prostaglandin H-2/thromboxane A(2) receptor antagon ist. 3. In the absence of extracellular Ca2+, bradykinin failed to induce contra ction. However, replenishing extracellular Ca2+ to 0.75 mm and higher induc ed an instantaneous contraction. However, replenishing Ca2+ per se did not induce any contraction in the absence of bradykinin. Pretreatment with eith er 10(-5) M 1-(beta-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenethyl)-1H-imi dazole hydrochloride (SKF96365) or 0.2 mM Ni2+ abolished the contraction in duced by bradykinin in the presence of extracellular Ca2+. 4. Treatment with 10(-5) M indomethacin completely inhibited the contractil e response induced by Ca2+ replenishment, regardless of the tuning of its a pplication, before or after the application of bradykinin. 5. In endothelial cells in the valvular strips, bradykinin caused a transie nt [Ca2+](i) elevation in the presence of 1.25 mM extracellular Ca2+, but [ Ca2+](i) returned to the resting level within 10 thin. Neither 10(-5) M SKF 96365 nor 0.2 mM Ni2+ had any effect oil the peak [Ca2+](i) elevation, but decreased [Ca2+](i) in the declining phase. In the absence of extracellular Ca2+, bradykinin induced a transient [Ca2+](i) elevation to a level simila r to that seen in the presence of 1.25 nM extracellular Ca2+. However, [Ca2 +](i) then rapidly returned to the prestimulation level within 5 min. Subse quent Ca2+ replenishment to 0.75 mm and higher in the presence of bradykini n elevated [Ca2+](i) to significantly higher levels than the resting level seen in the media containing 1.25 mM Ca2+. 6. In conclusion, Ca2+ influx in the endothelial cells is essential for bra dykinin to induce endothelium-dependent. contraction in the porcine interlo bar renal artery.