Modulation of skeletal muscle ca 2+ release channel activity by
sphingosine.
Needleman, Dolores H., Bahman Aghdasi, Alexander B. Seryshev, George
J. Schroepfer,jr. and Susan L. Hamilton.
The Department of Molecular Physiology and Biophysics, Baylor
College of Medicine, Houston,Tx,77030, the Department of
Biochemistry, Baylor College of Medicine, Houston, Tx, 77030 and the
Departments of Biochemistry and Cell Biology and of Chemistry, Rice
University, Houston, Tx,77251
APStracts 3:0306C, 1996.
The effect of D-erythro-C18-sphingosine (sphingosine) and related
compounds on the Ca2+ release channel (ryanodine binding protein) was
examined on rabbit skeletal muscle membranes, on the purified
ryanodine binding protein, and on the channel reconstituted into a
planar lipid bilayers. Sphingosine inhibited [3H]ryanodine binding to
sarcoplasmic reticulum (SR) membranes in a dose-dependent manner
similar to published results (Sabbadini et al. J. Biol. Chem.,
267:15475-15484,1992). The sphingolipid also inhibited [3H]ryanodine
binding to the purified ryanodine binding protein. Our results
demonstrate that the inhibition of [3H]ryanodine binding by
sphingosine is due to an increased rate of dissociation of bound
[3H]ryanodine from SR membranes and a decreased rate of association
of [3H]ryanodine to the high affinity site. Unlike other modulators
of the Ca2+ release channel, sphingosine can remove bound
[3H]ryanodine from the high affinity site within minutes. Sphingosine
increased the rate of dissociation of [3H]ryanodine bound to a
solubilized proteolytic fragment derived from the carboxyl terminus
of the ryanodine binding protein (cleavage at ARG 4475). Sphingosine
also inhibited the activity of the Ca2+ release channel incorporated
into planar lipid bilayers. Taken together, the data provide evidence
for a direct effect of sphingosine on the Ca2+ release channel.
Sphingosine is a noncompetitive inhibitor at the high affinity
ryanodine binding site and it interacts with a site between ARG 4475
and the carboxy terminus of the Ca2+ release channel.
Received 19 June 1996; accepted in final form 11 September 1996.
APS Manuscript Number C354-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996