CHARACTERISTICS OF HISTAMINE-H(1) RECEPTORS ON HELA-CELLS

The affinities of antagonists at histamine H-1 receptors on HeLa cells have been determined from inhibition of histamine-induced inositol ph osphate formation in intact cells and from inhibition of [H-3]mepyrami ne binding to HeLa cell membranes. The dissociation constants of mepyr amine and (+)-chlorpheniramine were similar to values for binding to H -1 receptors in other mammalian tissues, but much lower than the value s reported in an earlier study with [H-3]mepyramine and HeLa cell memb ranes. Evidence is presented that under the conditions employed in the earlier study the binding of [H-3]mepyramine is largely to secondary, non-H-1 receptor sites.