R. Kristipati et al., CHARACTERIZATION OF THE BINDING OF OMEGA-CONOPEPTIDES TO DIFFERENT CLASSES OF NON-L-TYPE NEURONAL CALCIUM CHANNELS, Molecular and cellular neurosciences, 5(3), 1994, pp. 219-228
The interaction of two synthetic omega-conopeptides SNX-111 (MVIIA) an
d SNX-230 (MVIIC) both derived from the marine snail Conus magus, with
non-L-type neuronal voltage-sensitive calcium channels (VSCC) in rat-
brain synaptosomal preparations has been investigated with the aid of
well-characterized I-125 derivatives of the two peptides. To assess th
e effects of iodination on the binding characteristics of SNX-111 and
SNX-230, the corresponding peptides containing monoiodotyrosine in pla
ce of tyrosine, namely, SNX-259 ([I-127]SNX-111) and SNX-260 ([I-127]S
NX-230), respectively, were prepared by solid-phase synthesis. Saturat
ion analysis showed that [I-125]SNX-111 and [I-125]SNX-230 bound to tw
o distinct classes of high-affinity sites with apparent K-d's Of 9 and
II pM and B-max's of 0.54 and 2.2 pmol/mg protein, respectively. Kine
tic analysis revealed that both peptides exhibited; high association r
ates as well as rapid dissociation rates in contrast to the I-125 deri
vative of the synthetic omega-conopeptide from Conus geographus, GVIA
(SNX-124), which binds irreversibly to N-type channels in rat brain sy
naptosomes. Competition binding experiments with [I-125]SNX-111 and [I
-125]SNX-124 established that both of them bind to the same site, name
ly, N-type VSCC. The site detected by the binding of [I-125]SNX-230 is
distinct from N-type VSCC since SNX-111 has very low affinity (K-i =
135 nM) in competition studies. Recent findings that a novel high-volt
age-activated calcium channel in rat cerebellar granule neurons is res
istant to blockers of L-, N-, and P-type VSCC but is highly sensitive
to SNX-230 suggest that the [I-125]SNX-230 binding site may represent
this novel type of calcium channel or another, as yet undescribed, VSC
C. (C) 1994 Academic Press, Inc.