Endothelin-1-Induced Contraction of Mesenteric Small Arteries Is Mediated by Ryanodine Receptor Ca2+ Channels and Cyclic ADP-Ribose

Contraction of vascular smooth muscle by endothelin-1 is dependent on extracellular and intracellular Ca. However, the role of ryanodine-sensitive Ca stores in endothelin-1-induced contraction is unknown. Vascular contraction was measured in mesenteric small arteries (200-300 μm intraluminal diameter) isolated from Sprague-Dawley rats and maintained at a constant intraluminal pressure of 40 mm Hg. The presence of functional ryanodine receptor Ca release channels (RyRC) was demonstrated by the finding that ryanodine (10 μM), which locks the RyRC in a subconductance state, produced significant contraction of small arteries in the presence of 15 mM KCl. This effect was inhibited by dantrolene (10 μM), a RyRC inhibitor. Dantrolene significantly reduced the ETA receptor-mediated contraction to endothelin-1 (10-10 M). The ability of dantrolene to reverse contraction induced by endothelin-1 was also determined. Dantrolene (1-10 μM) produced concentration-dependent relaxation of vessels precontracted to 38 ± 3% of resting diameter with endothelin-1 but had no effect in vessels precontracted to a similar degree with phenylephrine or KCl. Because activation of RyRC may be dependent on production of cyclic ADP-ribose, the effect of nicotinamide (2 mM), an inhibitor of ADP-ribosyl cyclase, on contraction to endothelin-1 was determined. Nicotinamide had an inhibitory effect similar to that produced by dantrolene. A combination of nicotinamide and dantrolene had no greater effect than either agent alone, suggesting a common pathway for cyclic ADP-ribose and RyRC. In summary, endothelin-1 induces contraction of small mesenteric arteries through ETA receptor-mediated production of cyclic ADP-ribose and activation of RyRC.