DHBP Block of Ryanodine Receptor Channels

Abstract

1,1′-diheptyl-4,4′-bipyridinium dibromide (DHBP), a divalent organic cation, was reported to inhibit muscle contraction, which was attributed to inhibition of ryanodine receptor (RyR) mediated Ca2+ release from the sarcoplasmic reticulum (SR). Still, single RyR channel studies are lacking and the mechanism by which DHBP blocks RyRs is unknown. We reconstituted RyRs from skeletal muscle and heart SR microsomes into planar bilayers. We observed with DHBP addition to the cytosolic surface of RyRs (clamped at Vm = 0 mV) decreased channel conductance (IC50 ∼ 1 mM). The percentage block in channel conductance elicited by DHBP was invariable in the range −30 to +30 mV. DHBP did not affect RyR gating characteristics, which was measured under Ca2+ conditions that produced low, moderate or high Po and in the presence/absence of physiological modulators (ATP, Mg2+). DHBP added to luminal and cytosolic sides of the RyRs, resulted in additive effects on channel conductance. DHBP also induced inhibition of RyR-mediated SR Ca2+ release from skeletal SR microsomes. A similar block of RyRs conductance was observed with other bipyridinum derivatives, none of which affected SERCA ATPase activity. Previous reports in the literature indicated block of RyRs by DHBP in cells required lower drug concentrations, suggesting a possible cellular mechanism of DHBP accumulation. In summary, DHBP blocks RyRs Ca2+ conductance resembling the action of polyamines and organic cations. DHBP properties make it an attractive experimental probe for understanding the role of RyR conductance in Ca2+ release from intracellular Ca2+ stores (Supported by American Heart Association and Eskridge Foundation).