[3H]noscapine binding sites in brain: relationship to indoleamines and the phosphoinositide and adenylyl cyclase messenger systems.

High affinity [3H]noscapine binding sites are brain specific, ion insensitive, and present in a variety of species and show strict structure-activity requirements. Among neurotransmitter-related structures, indoleamines and beta-carbolines display highest affinity for [3H]noscapine sites. Noscapine inhibits carbachol-stimulated phosphoinositide turnover in guinea pig and rat brain slices, with structural analogs possessing similar relative potencies for binding to [3H]noscapine binding sites and inhibiting phosphoinositide turnover. Noscapine and its derivatives also markedly enhance the ability of forskolin to augment cAMP levels in brain slices, with relative potencies paralleling affinities for noscapine binding sites.