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This article is part of the supplement: 18th Scientific Symposium of the Austrian Pharmacological Society (APHAR)

Open Access Meeting abstract

Low affinity histamine uptake into neonatal rat astrocytes does not involve OCT

Vesna Terbuc1, Maša Novak1, Katja Perdan-Pirkmajer1, Sergej Pirkmajer2 and Mojca Kržan1*

Author Affiliations

1 Department of Pharmacology and Experimental Toxicology Faculty of Medicine, University of Ljubljana, 1000 Ljubljana, Slovenia

2 Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, 1000 Ljubljana, Slovenia

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BMC Pharmacology and Toxicology 2012, 13(Suppl 1):A32  doi:10.1186/2050-6511-13-S1-A32


The electronic version of this article is the complete one and can be found online at: http://www.biomedcentral.com/2050-6511/13/S1/A32


Published:17 September 2012

© 2012 Terbuc et al; licensee BioMed Central Ltd.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background

Histamine is a double-protonated molecule with corresponding pKa values of 5.8 and 9.4. Therefore, at physiological pH, histamine exists as an equilibrium mixture of tautomeric cations: the monocation making up 96%, the dication only 3% and the rest being nonprotonated histamine. As a protonated molecule histamine most probably uses a carrier protein in order to cross the cell membrane. In the present work we wanted to determine the kinetic properties of histamine uptake and the influence of other biogenic amines on its transport.

Methods

We performed histamine uptake assays in the model system of cultured neonatal rat astrocytes. The mRNA expression of organic cation transporters (OCTs) was determined by qPCR. Student’s t-test was used for statistical analysis of uptake data.

Results

Histamine uptake in neonatal rat astrocytes is a bidirectional process, which was found to be dependent on pH and Na+, but not Cl-dependent, with low affinity (Km 116 µM) and high capacity (158 pmol/mg protein). The uptake was inhibited by millimolar concentrations of other biogenic amines (dopamine, noradrenaline and 5-hydroxytryptamine). The histamine metabolite tele-methylhistamine affected both directions of histamine uptake. In spite of the presence of OCT2 in neonatal astrocytes, the OCT inhibitors decynium-22 and corticosterone had no affect on histamine clearance.

Conclusions

Histamine is taken up into astrocytes by low-affinity high-capacity uptake, which involves transporter(s) other than OCT.

Acknowledgements

This work was supported by research grants from the Ministry of Higher Education, Science and Technology of Slovenia (P3-067).