κ-Opiate binding to rat brain and guinea pig cerebellum: Sensitivity towards ions and nucleotides

Abstract

Sodium ions and guanine nucleotides markedly affect the binding to μ and δ sites. Using the guinea pig cerebellum, a tissue whose opioid binding sites are almost exclusively κ, we have examined the sensitivity of [ 3H](−)-ethylketocyclazocine ([ 3H]EKC) binding to ions and guanine nucleotides. Unlike μ and δ binding, sodium ions and guanine nucleotides had little effect on the [ 3H]EKC binding in the guinea pig cerebellum. On the other hand, calcium and manganese at 1 mM lowered [ 3H]EKC binding in the guinea pig cerebellum by approximately 25%. Binding in rat brain, which was primarily μ and δ, was unaffected. These results point out additional biochemical differences between κ sites and the classic μ and δ binding sites.