Inhibition by cations of antagonist binding to histamine H<sub>1</sub>‐receptors: differential effect of sodium ions on the binding of two radioligands

1 The contractile action of the dipeptide carnosine (b-alanyl-L-histidine), active as a Zn·carnosine complex (Zn·Carn), was investigated in isolated rings of rabbit saphenous vein (RSV) and was found to be antagonized by the H 1 antagonist mepyramine. 2 Mepyramine-sensitive, histamine-induced contractures in RSV, were smaller (73+0.1%) and less well sustained than carnosine-induced contractures. In the radioligand binding assay, the e ect of carnosine can be described as a function of Zn·Carn concentration with an apparent logIC 50 of 75.61. This value is consistent with that obtained from the functional studies on RSV. 7 Histamine-induced contractures have an indomethacine-sensitive component (27.2+8.3% of control response), not apparent with carnosine-induced contractures. 8 Like histamine, carnosine evoked an H 2 -mediated (cimetidine-sensitive) relaxation in the presence of mepyramine, but was less potent (10.8+3.1% residual tension at 10 mM carnosine compared with 13.4+7.5% at 0.1 mM histamine). 9 Carnosine, like mepyramine, can`reveal' the H 2 -mediated relaxation of histamine providing further evidence that carnosine binds at the H 1 receptor. 10 We conclude that carnosine can act at the smooth muscle H 1 -receptor to provoke vasoconstriction and that it also has the potential to act at H 1 -receptors in CNS.

Section: Radioligand Binding Studiessupporting

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Analysis of an H₁ receptor‐mediated, zinc‐potentiated vasoconstrictor action of the histidyl dipeptide carnosine in rabbit saphenous vein

O'Dowd

Miller

1998

“…A better understanding of the significance of the modest Ca2+-dependence of the histamine-response in U373 MG cells will become clearer when selective blockade of the Ca2+-dependent component in brain tissue becomes possible. Neither L-type nor N-type Ca2+ channels appear to be involved and the use of divalent cations such as Ni2+ as non-selective blockers of Ca2+ entry is complicated by a possible additional action at the level of the HI-receptor, evident in the inhibition by Cd2+, Zn2+, Ni2+ and Co24 of [3H]-mepyramine binding to guinea-pig cerebellar membranes (Treherne et al, 1991). The secondary action of Ni24 on histamine-induced [3H]-IP, formation, without affecting the response to carbachol, has been demonstrated directly in HeLa cells, illustrating their utility as a model system (Arias-Montan-o & Young, 1993b).…”

Section: Discussionmentioning

confidence: 99%

Calcium‐dependence of histamine‐ and carbachol‐induced inositol phosphate formation in human U373 MG astrocytoma cells: comparison with HeLa cells and brain slices

Arias‐Montaño

Berger

Young

1994

Self Cite

Histamine (1 mm) induced an accumulation of inositol monophosphate ([3H]‐IP1) in the U373 MG human astrocytoma cell line which increased with time in the presence of 30 mm Li+. After a 30 min incubation period with 1 mm histamine [3H]‐IP1 was the major product detected (84 ± 1 % of total [3H]‐IPx) and was present at a level 11 (±1) fold of basal accumulation. Concentration‐response curves for histamine‐induced [3H]‐IP1 accumulation in U373 MG cells (EC50 5.4 ± 0.5 μm) were shifted to the right in a parallel fashion by mepyramine (slope of a Schild plot 0.99 ± 0.08), yielding a Kd for mepyramine of 3.5 ± 0.3 nm, consistent with the involvement of histamine H1‐receptors. The temelastine‐sensitive binding of [3H]‐mepyramine to a membrane fraction from U373 MG cells was hyperbolic and had a mean Kd of 2.5 ± 1.0 nm. The maximum amount of temelastine‐sensitive binding was 86 ± 19 pmol g−1 membrane protein. Carbachol also induced [3H]‐IP1 accumulation in U373 MG cells, 2.8 (± 0.1) fold of basal with 1 mm carbachol, with an EC50 of 48 ± 8 μm. Pirenzepine shifted carbachol concentration‐response curves to the right (slope of Schild plot 0.89 ± 0.07) giving a Kd for pirenzepine of 0.10 ± 0.01 μm, suggesting that phosphoinositide hydrolysis in U373 MG cells is mediated by the M3‐, rather than the M1‐, muscarinic receptor subtype. [3H]‐IP1 accumulation induced by both 1 mm histamine and by 1 mm carbachol increased when the Ca2+ concentration of the medium was increased from ‘zero’ (no added Ca2+) to 0.3 mm. Histamine‐stimulated [3H]‐IP1 accumulation was further increased, although not so markedly, as the Ca2+ was raised to 4 mm. The same pattern was apparent with histamine‐induced accumulations of [3H]‐IP2 and [3H]‐IP3. In contrast, [3H]‐IPx accumulation in response to carbachol increased between 0.3 and 1.3 mm, but thereafter remained unchanged ([3H]‐IP1) or declined ([3H]‐IP2 and [3H]‐IP3). In HeLa cells, [3H]‐IP1 accumulations induced by 1 mm histamine and 1 mm carbachol showed the same pattern of Ca2+ dependence and were independent of extracellular Ca2+ above 0.3 mm (histamine) or 1.3 mm (carbachol). The response to carbachol appeared to be mediated by an M3‐muscarinic receptor (apparent Kd for pirenzepine 0.09 μm). In cross‐chopped slices of guinea‐pig cerebral cortex and guinea‐pig cerebellum, [3H]‐IP1 accumulation induced by 1 mm histamine in the presence of 10 mm Li+ increased as the extracellular Ca2+ was increased from 0.3 to 2.5 mm, but a further increase to 4 mm had no further effect. In contrast the response to histamine in rat cerebral cortex increased markedly between 1.3 and 4 mm Ca2+. Accumulations of [3H]‐IP1 induced by carbachol in guinea‐pig or rat cerebral cortical slices were not increased as extracellular Ca2+ was raised from 0.3 to 4 mm. Nimodipine (100 nm) and ω‐conotoxin (3 μm) had no significant effect on histamine‐induced [3H]‐IP1 accumulation in rat cerebral cortical slices or in U373 MG cells. We conclude that histamine‐induced [3H]‐IP1 accumulation in U373 MG cells does appear to have a compo...

“…With the histamine HI-receptor the regulation of agonist binding by Na' (Chang & Snyder, 1980) presumably involves in the second transmembrane loop of the HI-receptor cloned from bovine adrenal medulla (Yamashita et al, 1991) or Asp-73 in the rat HI-receptor (Fujimoto et al, 1993). How-ever, antagonist binding can also be modulated by Na+, as originally demonstrated for opiate receptors (Pert & Snyder, 1974;Paterson et al, 1986), and we have reported that Na+ ions distinguish between the binding of two antagonist radioligands to the histamine HI-receptor (Treherne et al, 1991).…”

Section: Introductionmentioning

confidence: 79%

“…The structures of a number of the antagonists examined are shown in Figure 6. On the basis of the greater effect of Na' on the binding of [3H]-QMDP, a quaternary amine, than on the binding of [3H]-mepyramine, a tertiary amine, we suggested that the presence of the permanent positive charge might be an important factor (Treherne et al, 1991). However, the effect of Na' on the binding of norpirdonium and its quaternary derivative, pirdonium, is the reverse of what would have been predicted, since with this pair the shift of the inhibition curve for the tertiary amine is greater than with the permanently charged derivative.…”

Section: Discussionmentioning

confidence: 99%

Modulation of antagonist binding to histamine H₁‐receptors by sodium ions and by 2‐amino‐2‐hydroxymethyl‐propan‐1,3‐diol HCl

Gibson

Roques

Young

1994

Self Cite

NaCl (100 mm) reduced the potency of (+)‐N‐methyl‐4‐methyldiphenhydramine ((+)‐QMDP) as an inhibitor of the binding of [3H]‐mepyramine to histamine H1‐receptors on guinea‐pig cerebellar membranes to a greater extent than that of mepyramine, consistent with the greater inhibitory effect of Na+on the binding of [3H]‐QMDP than on the binding of [3H]‐mepyramine. The concentration of 2‐amino‐2‐hydroxymethyl‐propan‐1,3‐diol HCl (Tris, HCl) buffer, pH 7.5, present had little effect on the temelastine‐insensitive binding of [3H]‐mepyramine, but caused a concentration‐dependent inhibition of the binding of [3H]‐mepyramine sensitive to 1 μm temelastine (H1‐receptor binding), with an approximate IC50 of 75 mm, assuming that complete inhibition would have been achieved. Inhibition of [3H]‐mepyramine binding by Na+was more marked in 10 mm than in 50 mm Tris HCl and was not evident in 200 mm Tris HCl. The Kd for the temelastine‐sensitive binding of [3H]‐mepyramine measured in 10 mm Tris HCl, 0.24 ± 0.01 nm, was increased by 2.2 ± 0.2 fold by 100 mm NaCl, without any significant change in the maximum binding (Bmax). The Bmax for [3H]‐mepyramine was similarly unchanged in 50 mm Tris HCl, but the Kd was increased 2.5 ± 0.2 fold. The Kd for the temelastine‐sensitive binding of [3H]‐mepyramine was also increased in 50 mm, compared with 10 mm, N‐[2‐hydroxyethyl]piperazine‐N′‐[2‐ethanesulphonic acid] KOH (HEPES.KOH) buffer (Kd 0.25 ± 0.02 nm in 10 mm HEPES), but the evidence for an interaction between HEPES and Na+was less clear. The effect of 100 mm NaCl on the inhibition of [3H]‐mepyramine binding in 10 mm Tris HCl was examined for a range of antagonists. The decrease in potency caused by Na+was greatest for triprolidine, (+)‐chlorpheniramine and benzilylcholine (9.6–10.3 fold increase in Kd values) but the binding of mepyramine and promethazine was much less affected (1.8 and 1.9 fold increase in Kd respectively). The Kd for temelastine was not significantly changed. In contrast to the general decrease in antagonist affinity in the presence of Na+, the Kd for MDL 16,455A (4‐[1‐hydroxy‐4‐[4‐(hydroxydiphenylmethyl)‐1‐piperidinyl]butyl]‐α,α‐dimethylbenzene acetic acid) was increased, but only by 1.5 fold. It is concluded that Na+can act as an allosteric effector of the binding of antagonists at the histamine H1‐receptor. Tris HCl also appears to have an allosteric action at the H1‐receptor.