Binding of lanthanum ions and ruthenium red to synaptosomes and its effects on neurotransmitter release.
A technique for studying the binding of La3+ to synaptosomes in a double-beam spectrophotometer, using murexide as indicator, is described. The binding of La3+ was very rapid and Scatchard plots revealed two components, with KD values of 0.6 and 27 microM in a Na+-free medium (sucrose medium) and 2.3 and 63 microM in an ionic medium containing 135 mM Na+. The binding of the cationic dye ruthenium red (RuR) showed only one site, with a KD of 3.7 microM. La3+ binding was partially inhibited by RuR and vice versa, and La3+ was also capable of partially displacing RuR previously bound to the synaptosomes, particularly in the sucrose medium. The release of labeled gamma-aminobutyric acid (GABA) stimulated by K+ depolarization was inhibited by La3+ concentrations at or above 1 microM, in the ionic medium, whereas in the sucrose medium 2.5 microM or higher La3+ concentrations notably stimulated the spontaneous release of both GABA and glutamic acid. It is concluded that La3+ and RuR share at least one type of binding site, which is probably the high-affinity La3+ site. Since both La3+ and RuR at low concentrations have been shown to block the depolarization-induced Ca2+ entry in synaptosomes, this site might be related to the voltage-dependent Ca2+ entry involved in neurotransmitter release.
Tapia
R
R
Arias
C
C
Morales
E
E
D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D007700:Kinetics; D007811:Lanthanum / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D051379:Mice; D018377:Neurotransmitter Agents / Q000378:metabolism*; D009994:Osmolar Concentration; D012428:Ruthenium / Q000378:metabolism*; D012430:Ruthenium Red / Q000378:metabolism* / Q000494:pharmacology; D013395:Sucrose / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D018377:Neurotransmitter Agents; D012430:Ruthenium Red; D005680:gamma-Aminobutyric Acid; D013395:Sucrose; D007811:Lanthanum; D012428:Ruthenium