Structural Characteristics That Govern Binding to, and Modulation through, the Cardiac Ryanodine Receptor Nucleotide Binding Site

Comparative molecular field analysis (CoMFA) predicts that the large electrostatic field around the phosphate groups of ATP plays a crucial role in stabilizing the open state of the cardiac ryanodine receptor (RyR) channel. We therefore investigated the effects of adenosine-5-(,-methylenetriphosphate) (AMP-PCP), an ATP analog with lower negative charge in this region, on the gating of the cardiac RyR channel. In the presence of 10 M cytosolic Ca2, AMP-PCP exhibited approximately 50 % of the efficacy of ATP and optimal doses increased open proba-bility (Po) to only 0.441 0.156 (n 4), thus confirming the predictive ability of our preliminary CoMFA model. We also reveal that AMP-PCP has a higher affinity than ATP for the cardiac RyR, demonstrating that the structural properties re-quired for tight binding to RyR differ from those necessary fo