Role of cyclic ADP-ribose in Ca2+-induced Ca2+ release and vasoconstriction in small renal arteries.

Abstract Cyclic-ADP-ribose (cADPR) has been reported to serve as a second messenger to mobilize intracellular Ca 2+ independent of IP 3 in a variety of mammalian cells. This cADPR-mediated Ca 2+ signaling pathway importantly participates in the regulation of various cell functions. The present study determined the role of endogenous cADPR in mediating ryanodine-sensitive Ca 2+ -induced Ca 2+ release (CICR) in vascular myocytes from small renal arteries and vasomotor response of these arteries. In freshly-isolated renal arterial myocytes, addition of CaCl 2 (0.01, 0.1, and 1 mM) into the Ca 2+ -free bath solution produced a rapid Ca 2+ release response from the sarcoplasmic reticulum (SR), with a maximal increase of 237 ± 25 nM at 1 mM CaCl 2 . This CaCl 2 response was significantly blocked by a cell-membrane permeant cADPR antagonist, 8-bromo-cADP-ribose (8-br-cADPR) (30 μM) or ryanodine (50 μM). Caffeine, a classical CICR or ryanodine receptor activator was found to stimulate the SR Ca 2+ release (Δ[Ca 2+ ] i : 253 ± 35 nM), which was also attenuated by 8-br-cADPR or ryanodine. Using isolated and pressurized small renal arteries bathed with Ca 2+ -free solution, both CaCl 2 and caffeine-induced vasoconstrictions were significantly attenuated by either 8-br-cADPR or ryanodine. Biochemical analyses demonstrated that CaCl 2 and caffeine did not increase cADPR production in these renal arterial myocytes, but confocal microscopy showed that a dissociation of the accessory protein, FK506 binding protein 12.6 (FKBP12.6) from ryanodine receptors was induced by CaCl 2 . We conclude that cADPR importantly contributes to CICR and vasomotor responses of small renal arteries through enhanced dissociation of ryanodine receptors from their accessory protein.