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Re-examination of [3H]mepyramine binding assay for histamine H1 receptor using quinine
Y Q Liu1, Y Horio, H Mizuguchi
1Department of Pharmacology II, Faculty of Medicine, Osaka University, Suita, Japan.
Abstract:
[3H]Mepyramine, a potent antagonist of the histamine H1 receptor, has been widely used as a radioligand binding assay for the H1 receptor. Previously, we purified a mepyramine binding protein (MBP) from rat liver, but found that its partial amino acid sequences were very similar to those of debrisoquine 4-hydroxylase isozymes (P450 db1 and db2), which are members of the superfamily of cytochrome P450. Using cloned histamine H1 receptor cDNA, we found that [3H]mepyramine could bind only the H1 receptor and did not bind MBP in the presence of 10(-5) M quinine, an inhibitor of debrisoquine 4-hydroxylase isozymes. We developed a method to determine the contents of the H1 receptor and MBP separately using [3H]mepyramine and quinine and found that MBP is abundant in certain areas of bovine brain.
Insights
[3H]Mepyramine binds the histamine H1 receptor, not mepyramine binding protein (MBP). A new method distinguishes H1 receptor and MBP levels, revealing MBP
Area of Science:
- Biochemistry
- Pharmacology
- Neuroscience
Background:
- [3H]Mepyramine is a key radioligand for histamine H1 receptor studies.
- A previously purified mepyramine binding protein (MBP) shares sequence similarity with cytochrome P450 isozymes.
- Histamine H1 receptor and MBP binding characteristics needed clarification.
Purpose of the Study:
- To differentiate [3H]mepyramine binding between the histamine H1 receptor and MBP.
- To develop a method for quantifying H1 receptor and MBP levels.
- To investigate MBP distribution in bovine brain.
Main Methods:
- Utilized cloned histamine H1 receptor cDNA for binding studies.
- Employed quinine, an inhibitor of debrisoquine 4-hydroxylase isozymes, to differentiate binding.
- Developed a quantitative assay using [3H]mepyramine and quinine.
Main Results:
- [3H]Mepyramine selectively binds the histamine H1 receptor, not MBP, in the presence of quinine.
- A method was established to quantify H1 receptor and MBP levels separately.
- MBP was found to be abundant in specific regions of the bovine brain.
Conclusions:
- Quinine effectively distinguishes [3H]mepyramine binding to H1 receptors from MBP.
- The developed method allows for separate quantification of H1 receptors and MBP.
- MBP exhibits significant regional distribution in the bovine brain, suggesting potential functional roles.