ABSTRACT
This experimental study was designed to evaluate effects of hypo- and hyperthyroidism on the density of 3H-muscimol and 3H-diazepam-binding sites in synaptic membranes of the rat brain. It was shown that density of both 3H-muscimol and 3H-diazepam-binding sites increases in animals with hypothyroidism and decreases in hyperthyroidism. This difference may account for the predominance of general inhibitory reaction in animals with hypothyroidism and general excitation in hyperthyroid rats.
ABSTRACT
The Argiope lobata venom is shown to block synaptic potential at locust neuromuscular junctions and inhibit the high-affinity sodium independent L[3H]glutamate binding site in locust muscle membranes. The data obtained due to fractionation of venom evidence that it contains components which block synaptic potential and inhibit the binding of L[3H]glutamate (5 kDa and more) as well as components which block synaptic potential but do not inhibit the binding of L[3H]glutamate less than 5 kDa. These observations indicate that spider venom contains at least two components with different mechanism of action.
Subject(s)
Arthropod Venoms/pharmacology , Glutamates/metabolism , Neuromuscular Junction/metabolism , Spider Venoms/pharmacology , Animals , Binding, Competitive , Glutamic Acid , Grasshoppers , In Vitro Techniques , Molecular Weight , Neuromuscular Junction/drug effects , Spider Venoms/isolation & purificationABSTRACT
It has been shown that tetrodotoxin inhibits GABA-receptor binding of muscimol with solubilized membranes of the rat brain in a competitive manner, with the inhibition constant amounting to about 3 nM. Muscimol has been also demonstrated to competitively inhibit 3H-tetrodotoxin binding with the same drug.
Subject(s)
Muscimol/metabolism , Oxazoles/metabolism , Receptors, GABA-A/metabolism , Tetrodotoxin/metabolism , Animals , Binding, Competitive/drug effects , Brain/metabolism , Muscimol/antagonists & inhibitors , Rats , Solubility , Tetrodotoxin/antagonists & inhibitors , Tritium , gamma-Aminobutyric Acid/metabolismABSTRACT
The Na+-dependent and Na+-independent (receptor) binding of [3H] GABA is measured in rat brain synaptic membranes. The receptor binding is presented by at least 3 types of binding sites differing in kinetic parameters (dissociation constants and maximal concentration of binding sites). Phenyl-GABA and pyracetam do not affect receptor binding while 4-hydroxybutyric acid, apamine and bicuculline inhibit it with inhibition constants K1=100, 2 and 1 micron, respectively. Solubilization of synaptic membranes with 2% potassium cholate in the presence of total brain phospholipids does not inactivate [3H] GABA receptor binding.
