[₃H]‐(+)‐N‐methyl‐4‐methyldiphenhydramine, a quaternary radioligand for the histamine H₁‐receptor

Inhibition by cations of antagonist binding to histamine H1‐receptors: differential effect of sodium ions on the binding of two radioligands

“…In contrast, the binding of [3H]-mepyramine, an antagonist, is reported to be relatively unaffected by these cations (Chang & Snyder, 1980 reduced by 100mM NaCl (Treherne & Young, 1988a). We describe here the results of a more extensive study of the effect of cations on the binding of [3H]-QMDP and [3H]-mepyramine.…”

“…We describe here the results of a more extensive study of the effect of cations on the binding of [3H]-QMDP and [3H]-mepyramine. Both of these compounds have the 'classical' antihistamine structure (Figure 1), are a similar size and have a similar affinity for the Hl-receptor, Kd circa 1 nM (Treherne & Young, 1988a). We show that the binding of both [3H]- QMDP and [3H]-mepyramine is inhibited by a range of mono-and divalent cations, but that Na+ distinguishes between the binding of the two radioligands.…”

“…A set of incubations with 100mm NaCl was included occasionally in experiments with other metal salts in order to check the consistency of the effects of ions. Non-H1-receptor binding (non-specific binding) was determined as the binding insensitive to inhibition by 1FIM temelastine, which has a low affinity for secondary, non-H1-receptor, binding sites for [3H]-QMDP (Treherne & Young, 1988a (Treherne & Young, 1988a and makes it probable that it is largely or wholly a property of the cation. Direct comparison in 3 experiments of the inhibitory effects of NaCl, Na2SO4 and NaNO3, equimolar with respect to Na', failed to show any consistent difference between the different salts.…”

Characteristics of the binding of [3H]‐mepyramine to intact human U373 MG astrocytoma cells: evidence for histamine‐induced H1‐receptor internalisation

“…The potential difficulties in using cell-permeable radioligands for the measurement of binding to cell surface receptors were documented some years ago (Maloteaux et al, 1983) and initially we set out to circumvent them by synthesizing a nonpenetrant radioligand for the histamine HI-receptor, Pfjl-QMDP, a quaternary amine, (Treherne & Young, 1988a), in analogy to the use of PH]-N-methylscopolamine (Galper et al, 1982) and CGP-12177 (Hertel et al, 1983a) (Chang et al, 1979;Hill & Young, 1981), and such sites are present, although not always recognised as such, in the DDT1MF2 (Mitsuhashi & Payan, 1988), HeLa (Raymond et al, 1991;Arias-Montafio & Young, 1993) and P19 (Bloemers et al, 1993) (Leurs et al, 1989), which appears to be a member of the cytochrome P450 family (Liu et al, 1992). However, this site was not evident in brain membranes (Liu et al, 1992) (Hertel et al, 1983a;Waldo et al, 1983) and muscarinic receptors (Koenig & Edwardson, 1994, and references therein).…”

“…However, although there have been Cowlen et al, 1990;Smit et al, 1992;Bristow & 7amani, 1993; numerous studies of the mechanisms involved in the desensi- Dickenson & Hill, 1993;McCreath et al, 1994), a number of tization of responses to histamine at Hi-receptors in intestinal which have provided evidence for changes at the level of the smooth muscle (Barsoum & Gaddum, 1935;Cantoni & Eastreceptor (Brown et al, 1986;Nakahata & Harden, 1987;Hishinuma & Uchida, 1988;Cowlen et al, 1990;Horio et al, 1990b; Leurs et al, 1990;Dickenson & Hill, 1993) which will cross the cell membrane and bind to intracellular IkkW Joumal of Pharmacoloa (1995) 116, 2715-2723 sites and become concentrated in compartments with a low pH, have been noted some years ago (Maloteaux et al, 1983). We have attempted to avoid these difficulties by synthesizing a quaternary amine radioligand for the H1-receptor, [3H]-(+)-N-methyl-4-methyldiphenhydramine ([3H]-QMDP), which should bind only to sites on the plasma membrane (Treherne & Young, 1988a (Wallace & Young, 1983;Treherne & Young, 1988b), which should allow extensive washing of cells, and (b) the availability of non-penetrant and penetrant HI-receptor antagonists, which might be used to determine binding to plasma membrane HI-receptors and plasma membrane+ intracellularreceptors, respectively. We describe here a study of the characteristics of the binding of [3H]-mepyramine to intact human U373 MG astrocytoma cells, which possess histamine HI-receptors coupled to the activation of phosphoinositidase C (Arias-Montafio et al, 1994), and the effect on [3H]-mepyramine binding of pre-exposure of the cells to a high concentration of histamine.…”