Ca2+ and voltage dependence of cardiac ryanodine receptor channel block by sphingosylphosphorylcholine.
The effect of sphingosylphosphorylcholine (SPC) on the cytoplasmic Ca(2+) and voltage dependence of channel gating by cardiac ryanodine receptors (RyR) was examined in lipid bilayer experiments. Micromolar concentrations of the lysosphingolipid SPC added to cis solutions rapidly and reversibly decreased the single-channel open probability (P(o)) of reconstituted RyR channels. The SPC-induced decrease in P(o) was marked by an increase in mean closed time and burst-like channel gating. Gating kinetics during intraburst periods were unchanged from those observed in the absence of the sphingolipid, although SPC induced a long-lived closed state that appeared to explain the observed decrease in channel P(o). SPC effects were observed over a broad range of cis [Ca(2+)] but were not competitive with Ca(2+). Interestingly, the sphingolipid-induced, long-lived closed state displayed voltage-dependent kinetics, even though other channel gating kinetics were not sensitive to voltage. Assuming SPC effects represent channel blockade, these results suggest that the blocking rate is independent of voltage whereas the unblocking rate is voltage dependent. Together, these results suggest that SPC binds directly to the cytoplasmic side of the RyR protein in a location in or near the membrane dielectric, but distinct from cytoplasmic Ca(2+) binding sites on the protein.
Yasukochi
Midori
M
Laboratory of Human Biology, School of Medicine, Fukuoka University, 45-1, 7-chome Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan.
Uehara
Akira
A
Kobayashi
Sei
S
Berlin
Joshua R
JR
D000818:Animals; D002118:Calcium / Q000378:metabolism; D006321:Heart / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects*; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology*
D008051:Lipid Bilayers; D019837:Ryanodine Receptor Calcium Release Channel; C005356:sphingosine phosphorylcholine; D010767:Phosphorylcholine; D013110:Sphingosine; D002118:Calcium