The interaction of a neutral ryanoid with the ryanodine receptor channel provides insights into the mechanisms by which ryanoid binding is modulated by voltage.
In an earlier investigation, we demonstrated that the likelihood of interaction of a positively charged ryanoid, 21-amino-9alpha-hydroxyryanodine, with the sarcoplasmic reticulum Ca(2+)-release channel (ryanodine receptor, RyR) is dependent on holding potential (Tanna, B., W. Welch, L. Ruest, J.L. Sutko, and A. J. Williams. 1998. J. Gen. Physiol. 112:55-69) and suggested that voltage dependence could result from either the translocation of the charged ligand to a site within the voltage drop across the channel or a voltage-driven alteration in receptor affinity. We now report experiments that allow us to assess the validity of these alternate mechanisms. Ryanodol is a neutral ryanoid that binds to RyR and induces modification of channel function. By determining the influence of transmembrane potential on the probability of channel modification by ryanodol and the rate constants of ryanodol association and dissociation, we demonstrate that the influence of voltage is qualitatively the same for both the neutral and positively charged ryanoids. These experiments establish that most, if not all, of the modification of ryanoid interaction with RyR by transmembrane holding potential results from a voltage-driven alteration in receptor affinity.
Tanna
B
B
Department of Cardiac Medicine, National Heart & Lung Institute, Imperial College of Science, Technology & Medicine, London SW3 6LY, United Kingdom.
Welch
W
W
Ruest
L
L
Sutko
J L
JL
Williams
A J
AJ
D000818:Animals; D008564:Membrane Potentials / Q000502:physiology; D012433:Ryanodine / Q000031:analogs & derivatives* / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D012756:Sheep
C113821:21-amino-9-hydroxyryanodine; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine