Specific binding of L-triiodothyronine modulates Na⁺-K⁺- ATPase activity in adult rat cerebrocortical synaptosomes

Abstract

Interactions of L-triiodothyronine (T₃) in adult rat cerebrocortical synaptosomes were studied in vitro. Scatchard plot analysis revealed two sets of T₃ binding sites. The degree of saturation of T₃ binding sites (putative receptor) correlated well with the dose-dependent inhibition of Na⁺-K⁺-ATPase activity in synaptosomes. The relative binding affinities and relative inhibition of enzyme activities for different TH analogues were L-T₃>T₃-amine>TRIAC=L-T₄>r-T₃>T₂ and L-T₃>T₃-amine>TRIAC>L-T₄>r-T₃>T₂, respectively. The present study demonstrates the nature of inhibition of synaptosomal Na⁺-K⁺-ATPase activity may be as a function of T₃ occupancy of synaptosomal receptor sites in adult mammalian brain.