In vitro effect of lithium on alpha2D‐adrenoceptors binding in rat cerebral cortex

Abstract

The aim of this study was to examine the effect of lithium on the density and the affinity of rat α2D-adrenoceptors (α2D-AR) in our experimental model. Sodium, which has been reported to modulate certain adrenoceptors, was also used. Rat cerebral cortex slices were incubated with increasing concentrations of LiCl (0.5 − 100 x 10−3 M) or NaCl (1 − 100 x 10−3 M) at 37°C for 10 min and [3H]yohimbine saturation experiments were then carried out. In untreated tissue the density and the affinity of [3H]yohimbine binding sites were 197.8 ± 16.9 fmol/mg protein and 8.55 ± 1.0 nM, respectively. ANOVA analysis revealed that the [3H]yohimbine dissociation constant in lithium- and sodium-incubated tissues was similar to that in untreated samples (F6, 23 = 0.700; p= 0,654 for lithium; F3, 15 = 0.334; p=0.801 for sodium). Moreover, neither lithium nor sodium treatment affected the density of [3H]yohimbine binding sites (F6, 23 = 2.411; p=0.072 for lithium: F3, 15=1.204; p=0.350 for sodium). Although it has been reported an allosteric modulation of α2-AR binding by monovalent cations, our data show that the affinity and density values of α2D-AR for [3H]yohimbine in the presence of LiCl or NaCl were not modified in our experiemental model. Density of α2D-AR (fmol/mg prot) ± SEM (n = 5–9).