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The Scientific World Journal
Volume 2012, Article ID 524169, 7 pages
Research Article

Fluorescence Correlation Spectroscopy in Drug Discovery: Study of Alexa532-Endothelin 1 Binding to the Endothelin ETA Receptor to Describe the Pharmacological Profile of Natural Products

1Department of Molecular Pharmacology and Pharmacognosy, Drug Discovery Center, Institute for Scientific Research and High Technology Services, P.O. Box 0843-01103, Panama, Panama
2Smithsonian Tropical Research Institute, P.O. Box 0843-03092, Panama, Panama
3Institute of Biochemistry and Molecular Biology, Rheinische Friedrich-Wilhelms-University, Nussallee 11, 53115 Bonn, Germany
4Department of Plant Biology, University of Illinois at Urbana-Champaign, Room 265, Morrill Hall, 505 S. Goodwin Avenue, Urbana, IL 61801, USA

Received 19 October 2011; Accepted 12 December 2011

Academic Editor: Soichi Miwa

Copyright © 2012 Catherina Caballero-George et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Fluorescence correlation spectroscopy and the newly synthesized Alexa532-ET1 were used to study the dynamics of the endothelin ETA receptor-ligand complex alone and under the influence of a semisynthetic selective antagonist and a fungal extract on living A10 cells. Dose-dependent increase of inositol phosphate production was seen for Alexa532-ET1, and its binding was reduced to 8% by the selective endothelin ETA antagonist BQ-123, confirming the specific binding of Alexa532-ET1 to the endothelin ETA receptor. Two different lateral mobilities of the receptor-ligand complexes within the cell membrane were found allowing the discrimination of different states for this complex. BQ-123 showed a strong binding affinity to the “inactive” receptor state characterized by the slow diffusion time constant. A similar effect was observed for the fungal extract, which completely displaced Alexa532-ET1 from its binding to the “inactive” receptor state. These findings suggest that both BQ-123 and the fungal extract act as inverse agonists.