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 extra cellular and intracellular Ca2+. However, the role of ryanodine-sensitive C a2+ stores in endothelin-1-induced contraction is unknown. Vascular contrac tion was measured in mesenteric small arteries (200-300 mum intraluminal di ameter) isolated from Sprague-Dawley rats and maintained at a constant intr aluminal pressure of 40 mm Hg. The presence of functional ryanodine recepto r Ca2+ release channels (RyRC) was demonstrated by the finding that ryanodi ne (10 muM), which locks the RyRC in a subconductance state, produced signi ficant contraction of small arteries in the presence of 15 mM KCl. This eff ect was inhibited by dantrolene (10 muM), a RyRC inhibitor. Dantrolene sign ificantly reduced the ETA receptor-mediated contraction to endothelin-1 (10 (-11) -10(-9) M). The ability of dantrolene to reverse contraction induced by endothelin-1 was also determined. Dantrolene (1-10 muM) produced concent ration-dependent relaxation of vessels precontracted to 38 +/- 3% of restin g 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 pro duced by dantrolene. A combination of nicotinamide and dantrolene had no gr eater effect than either agent alone, suggesting a common pathway for cycli c ADP-ribose and RyRC. In summary, endothelin-1 induces contraction of smal l mesenteric arteries through ETA receptor-mediated production of cyclic AD P-ribose and activation of RyRC.