Comparison of the contractile and calcium-increasing properties of platelet-activating factor and endothelin-1 in the rat mesenteric artery and vein

摘要

class="enumerated" style="list-style-type:decimal">In the present study, the properties of endothelin-1 (ET-1) and platelet-activating factor (PAF) in inducing contraction and increased intracellular-free calcium level in rat mesenteric arteries and veins were studied. Furthermore, measurements of cytosolic ([Ca]c) and nuclear ([Ca]n) Ca²⁺ were performed by confocal microscopy.PAF, at a concentration of 1 μM, and the selective ETB agonists, IRL-1620 and sarafotoxin S6C (100 nM), induced a marked constriction and increase in [Ca]i in the mesenteric vein but not in the artery. On the other hand, endothelin-1 (1–100 nM) induced a significant concentration-dependent nifedipine-insensitive increase in tension and [Ca]i in both arteries and veins.Those responses to endothelin-1 were significantly reduced by the ETA receptor antagonist, BQ-123 (10⁻⁶ M), on both types of vessels, whereas the selective ETB receptor antagonist, BQ-788, inhibited only the venous responses. The mixed ETA/ETB receptor antagonist, SB 209670, reduced the ET-1-induced venous responses to the same level of that found in presence of BQ-123 or BQ-788. However, concomitant applications of BQ-123 and BQ-788 reduced the vasoconstriction below to that induced by ETA or ETB blockade without further affecting [Ca]i.PAF and the selective ETB agonists IRL-1620, induced a sustained increase of [Ca]c and [Ca]n solely in venous cells and ET-1 in both arterial and venous smooth muscle cells.Thus, PAF increases total intracellular calcium concentration and tension on the smooth muscle cells from venous origin only. Furthermore, ET-1-induced vasoactive as well as [Ca]i and [Ca]_n increasing effects are mediated by distinct receptors on venous and arterial smooth muscles.