Kappa binding sites in guinea-pig brain membranes: evidence for a dynorphin-resistant subtype

Using [3H]ethylketocyclazocine after suppression of mu, delta and sigma binding by 100 nM DAGO + 100 nM DADLE + 10 microM phencyclidine we showed the existence of a subclass of kappa sites insensitive to dynorphins 1-9 and 1-17, and alpha and beta neoendorphins, but sensitive to the non-peptidic opiates. The dynorphin-sensitive site probably corresponds to the "standard" kappa site while the importance of the dynorphin-resistant site remains to be established.