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Structural factors that determine the ability of adenosine and related compounds to activate the cardiac ryanodine receptor
Author(s) -
Chan Wei Mun,
Welch William,
Sitsapesan Rebecca
Publication year - 2000
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0703459
Subject(s) - ryanodine receptor , agonist , adenosine , chemistry , gating , partial agonist , adenosine triphosphate , biophysics , gtp' , stereochemistry , adenosine diphosphate , biochemistry , endoplasmic reticulum , receptor , medicine , biology , enzyme , platelet , platelet aggregation
The effects of adenosine and adenine on the gating of native sheep cardiac ryanodine receptor (RyR) channels were investigated. By examining the mechanisms underlying channel activation and by using comparative molecular field analysis (CoMFA) we have investigated the structural features of adenine‐based ligands involved in channel activation. In the presence of 10 μ M cytosolic Ca 2+ , adenosine and adenine both activate the channel but only to a level approximately 10 and 20% respectively of that of ATP indicating that both are partial agonists of low efficacy. Adenosine was able to antagonize the ATP‐induced increase in open probability (Po) as expected for a partial agonist of low efficacy at the ATP sites on the cardiac RyR. GTP (100 μ M –10 m M ) had no effect on channel gating indicating that the adenine ring structure is important for agonist activity at the ATP‐sites on RyR. CoMFA revealed an extremely strong correlation between the structural features of the five ATP analogues and the ability to increase (Po). Our model indicates that the high efficacy of ATP results primarily from the large electrostatic field established by the ionized phosphate groups. Reducing the number of phosphate groups lowers the strength of this field, leading to ligands with lower efficacy. In addition, steric interactions between the α‐phosphate and ribose moieties and the RyR are correlated with low Po.British Journal of Pharmacology (2000) 130 , 1618–1626; doi: 10.1038/sj.bjp.0703459