CHARACTERISTICS OF [H-3] MEPYRAMINE BINDING IN DDT(1)MF-2 CELLS - EVIDENCE FOR HIGH-AFFINITY BINDING TO A FUNCTIONAL HISTAMINE-H-1 RECEPTOR

The binding characteristics of [H-3]mepyramine to histamine H-1 receptors in the smooth muscle cell line, DDT(1)MF-2, have been investigated. Competition binding experiments produced dissociation constants (K-i) for mepyramine, (+)-chlorpheniramine, and promethazine of 3.4 nM, 2.6 nM and 0.66 nM, respectively. Saturation binding using [H-3]mepyramine produced a K-d of 2.1 nM and a B-max of 47 fmol/mg protein. These data suggest that a high-affinity [H-3]mepyramine binding site can be detected with the characteristics of the ''classical'' histamine H-1 receptor. The low-affinity [H-3]mepyramine binding site reported previously [Mitsuhashi, M, and Payan, D.G. (1988) J. Cell. Physiol. 134, 367-375] is predominantly to a secondary [H-3]mepyramine site. The ''low affinity'' or secondary [H-3]mepyramine binding site on DDT(1)MF-2 cells is insensitive to quinine (10 mu M) and is therefore distinct from the [H-3]mepyramine binding protein found in rat liver.