Effects of Cations and Anions on the Binding of 3H-Diazepam to Rat Brain

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Abstract
Crude synaptic membranes from whole rat brain were prepared by differential centrifugation followed by hypo-osmotic shock and freezing. The monovalent cations (as their chloride salts) Li+, Na+, K+ and NH4+ produced very slight enhancements of binding of diazepam [CNS depressant] whereas Cs+ did not have any effect. The monovalent anions (as their Na salts) F- and I- were inhibitory whereas Br- produced a very slight enhancement. Divalent cations (as their chloride salts) produced marked enhancements of binding. Ni2+ caused the greatest increase which reached 86% at 5 mM. This increased binding was the result of enhanced affinity for the binding site; the total number of sites was not altered. The rank order of potency for stimulating binding at 0.1 mM cation concentration was Ni2+, Hg2+ > Cu2+, Zn2+ > Co2+ > Ba2+, Mg2+, Ca2+, Mn2+. Ni2+ did not affect the specific binding to brain homogenates of 3H-strychnine or of 3H-quinuclidinyl benzilate, but inhibited binding of 3H-naloxone.