ACTIVATION OF THE SKELETAL-MUSCLE RYANODINE RECEPTOR BY SURAMIN AND SURAMIN ANALOGS

Ca2+ release from skeletal muscle sarcoplasmic reticulum is activated by adenine nucleotides and suramin. Because suramin is known to intera ct with ATP-binding enzymes and ATP receptors (P-2-purinergic receptor s), the stimulation by suramin has been postulated to occur via the ad enine nucleotide-binding site of the ryanodine receptor/Ca2+-release c hannel. We tested this hypothesis using suramin and the following sura min analogs: NF037, NF018, NF023, and NF007. The suramin analogs stimu late the binding of [H-3]ryanodine binding to sarcoplasmic reticulum m embranes with the following rank order of potency: suramin (EC(50) = s imilar to 60 mu M) > NF037 (EC(50) = similar to 150 mu M) > NF018 > NF 023 > NF007. The suramin-induced stimulation occurs via a myoplasmic b inding site on the ryanodine receptor as confirmed by binding experime nts and single-channel recordings with the purified protein. This bind ing site is different than that for ATP, a conclusion that is supporte d by the following observations: (i) Suramin stimulates the associatio n rate and inhibits the dissociation rate of [H-3]ryanodine, whereas A TP analogs increase only the on-rate. (ii) In the presence of suramin but not of ATP analogs, [H-3]ryanodine binding is resistant to the inh ibitory effect of millimolar Mg2+ and Ca2+. (iii) ATP analogs and sura min have an additive effect on [H-3]ryanodine binding. (iv) Affinity l abeling of the purified ryanodine receptor with 2',3'-dialdehyde [alph a-P-32]ATP or after in situ oxidation of [gamma-P-32]ATP is not affect ed by suramin. Thus, our results show that suramin acts as a direct an d potent stimulator of the ryanodine receptor but that this action is mediated via a binding site different from that for adenine nucleotide s.