Regulation of the calcium release channel from skeletal muscle by suramin and the disulfonated stilbene derivatives DIDS, DBDS, and DNDS

Activation of skeletal muscle ryanodine receptors (RyRs) by suramin and disulfonic stilbene derivatives (Diisothiocyanostilbene-2',2'-disulfonic acid (DIDS), 4,4'-dibenzamidostilbene-2,2'-disulfonic acid (DBDS),and 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS)) was investigated using planar bilayers. One reversible and two nonreversible mechanisms were identified. Ka for reversible activation (∼100 μM) depended on cytoplasmic [Ca²⁺] and the bilayer composition.Replacement of neutral lipids by negative phosphatidylserine increased Ka fourfold, suggesting that reversible binding sites are near the bilayer surface. Suramin and the stilbene derivatives adsorbed to neutral bilayers with maximal mole fractions between 1–8% and with affinities ∼100 μM but did not adsorb to negative lipids. DIDS activated RyRs by two nonreversible mechanisms, distinguishable by their disparate DIDS binding rates (10⁵ and 60 M⁻¹ s⁻¹) and actions. Both mechanisms activated RyRs via several jumps in open probability, indicating several DIDS binding events. The fast and slow mechanisms are independent of each other, the reversible mechanism and ATP binding. The fast mechanism confers DIDS sensitivity∼ 1000-fold greater than previously reported, increases Ca²⁺ activation and increases Ki for Ca²⁺ /Mg²⁺ inhibition 10-fold. The slow mechanism activates RyRs in the absence of Ca²⁺and ATP, increases ATP activation without altering Ka, and slightly increases activity at pH 6.5. These findings explain how different types of DIDS activation are observed under different conditions.