cADP-ribose activates reconstituted ryanodine receptors from coronary arterial smooth muscle

The present study was designed to test the hypothesis that cADP-ribose (cADPR) increases Ca2+ release through activation of ryanodine receptors (RYR) on the sarcoplasmic reticulum (SR) in coronary arterial smooth muscle cells (CASMCs). We reconstituted RYR from the SR of CASMCs into planar lipid bilayers and examined the effect of cADPR on the activity of these Ca2+ release channels. In a symmetrical cesium methanesulfonate configuration, a 245 pS Cs+ current was recorded. This current was characterized by the formation of a subconductance and increase in the open probability (NPo) of the channels in the presence of ryanodine (0.01-1 muM) and imperatoxin A (100 nM). A high concentration of ryanodine (50 muM) and ruthenium red (40-80 muM) substantially inhibited the activity of RYR/Ca2+ release channels. Caffeine (0.5-5 mM) markedly increased the NPo of these Ca2+ release channels of the SR, but D-myoinositol 1,4,5-trisphospate and heparin were without effect. Cyclic ADPR significantly increased the NPo of these Ca2+ release channels of SR in a concentration-dependent manner. Addition of cADPR (0.01 muM) into the cis bath solution produced a 2.9-fold increase in the NPo of these RYR/Ca2+ release channels. An eightfold increase in the NPo of the RYR/Ca2+ release channels (0.0056 +/- 0.001 vs. 0.048 +/- 0.017) was observed at a concentration of cADPR of 1 muM. The effect of cADPR was completely abolished by ryanodine (50 muM). In the presence of cADPR, Ca2+-induced activation of these channels was markedly enhanced. These results provide evidence that cADPR activates RYR/Ca2+ release channels on the SR of CASMCs. It is concluded that cADPR stimulates Ca2+ release through the activation of RYRs on the SR of these smooth mucle cells.