Premium
Binding of Lanthanum Ions and Ruthenium Red to Synaptosomes and Its Effects on Neurotransmitter Release
Author(s) -
Tapia Ricardo,
Arias Clorinda,
Morales Ezequiel
Publication year - 1985
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1985.tb07213.x
Subject(s) - lanthanum , neurotransmitter , ruthenium red , ruthenium , chemistry , ion , biophysics , biochemistry , calcium , inorganic chemistry , biology , receptor , organic chemistry , catalysis
A technique for studying the binding of La 3+ to synaptosomes in a double‐beam spectrophotometer, using murexide as indicator, is described. The binding of La 3+ was very rapid and Scatchard plots revealed two components, with K D values of 0.6 and 27 μ M in a Na + ‐free medium (sucrose medium) and 2.3 and 63 μ M in an ionic medium containing 135 m M Na + . The binding of the cationic dye ruthenium red (RuR) showed only one site, with a K D of 3.7 μ M. La 3+ binding was partially inhibited by RuR and vice versa, and La 3+ was also capable of partially displacing RuR previously bound to the synaptosomes, particularly in the sucrose medium. The release of labeled γ‐aminobutyric acid (GABA) stimulated by K + depolarization was inhibited by La 3+ concentrations at or above 1 μ M. in the ionic medium, whereas in the sucrose medium 2.5 μ M or higher La 3+ concentrations notably stimulated the spontaneous release of both GABA and glutamic acid. It is concluded that La 3+ and RuR share at least one type of binding site, which is probably the high‐affinity La 3+ site. Since both La 3+ and RuR at low concentrations have been shown to block the depolarization‐induced Ca 2+ entry in synaptosomes, this site might be related to the voltage‐dependent Ca 2+ entry involved in neurotransmitter release.