Kappa-opiate binding to rat brain and guinea pig cerebellum: sensitivity towards ions and nucleotides

Sodium ions and guanine nucleotides markedly affect the binding to mu and delta sites. Using the guinea pig cerebellum, a tissue whose opioid binding sites are almost exclusively kappa, we have examined the sensitivity of [3H](-)-ethylketocyclazocine ([3H]EKC) binding to ions and guanine nucleotides. Unlike mu and delta 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 mu and delta, was unaffected. These results point out additional biochemical differences between kappa sites and the classic mu and delta binding sites.