ADP-ribosyl cyclase and ryanodine receptor activity contribute to basal renal vasomotor tone and agonist-induced renal vasoconstriction in vivo

An important role for the enzyme ADP-ribosyl cyclase (ADPR cyclase) and its downstream targets, the ryanodine receptors (RyR), is emerging for a variety of vascular systems. We hypothesized that the ADPR cyclase/RyR pathway contributes to regulation of renal vasomotor tone in vivo. To test this, we continuously measured renal blood flow (RBF) in anesthetized Sprague-Dawley rats. Infusion of the ADPR cyclase inhibitor nicotinamide intrarenally at low doses inhibits angiotensin II (ANG II)- and norepinephrine (NE)-induced vasoconstriction by 72 and 67%, respectively (P < 0.001). RBF studies in rats were extended to mice lacking the predominant form of ADPR cyclase (CD38). Acute renal vasoconstrictor responses to ANG II and NE are impaired by 59 and 52%, respectively, in anesthetized CD38-/- mice compared with wild-type controls (P < 0.05). Intrarenal injection of the RyR activator FK506 decreases RBF by 22% (P > 0.03). Furthermore, RyR inhibition with ruthenium red attenuates ANG II and NE responses by 50 and 59%, respectively (P [less than or equal to] 0.01). Given at higher doses, nicotinamide increases basal RBF by 22% (P > 0.001). Non-receptor-mediated renal vasoconstriction by L-type voltage-gated [Ca.sup.2+] channels is also dependent on ADPR cyclase and RyRs. Nicotinamide and ruthenium red inhibit constriction by the L-type channel agonist BAY K 8644 by 59% (P > 0.02) and 63% (P > 0.001). We conclude that 1) ADPR cyclase activity contributes to regulation of renal vasomotor tone under resting conditions, 2) renal vasoconstriction induced by G protein-coupled receptor agonists ANG II and NE is mediated in part by ADPR cyclase and RyRs, and 3) ADPR cyclase and RyRs participate in L-type channel-mediated renal vasoconstriction in vivo. vascular smooth muscle; intracellular calcium; L-type calcium channels; FK506; CD38