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Volume changes of individual melanosomes measured by scanning force microscopy
Linköping University, Department of Biomedical Engineering. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Medicine and Care, Pharmacology. Linköping University, Faculty of Health Sciences.
2001 (English)In: Pigment Cell Research, ISSN 0893-5785, E-ISSN 1600-0749, Vol. 14, no 6, 445-449 p.Article in journal (Refereed) Published
Abstract [en]

Black pigment cells, melanophores, e.g. located in the epidermis and dermis of frogs, are large flat cells having intracellular black pigment granules, called melanosomes. Due to a large size, high optical contrast, and quick response to drugs, melanophores are attractive as biosensors as well as for model studies of intracellular processes; e.g. organelle transport and G-protein coupled receptors. The geometry of melanosomes from African clawed toad, Xenopus laevis, has been measured using scanning force microscopy (SFM). Three-dimensional images from SFM were used to measure height, width, and length of the melanosomes (100 from aggregated cells and 100 from dispersed cells). The volumes of melanosomes isolated from aggregated and dispersed melanophores were significantly different (P<0.05, n=200). The average ellipsoidal volume was 0.14±0.01 (aggregated) and 0.17±0.01 μm3 (dispersed), a difference of 18%. The average major diameter was 810±20 and 880±20 nm for aggregated and dispersed melanosomes, respectively. To our knowledge, this is the first time SFM has been used to study melanosomes. This may provide an alternative non-destructive technique that may be particularly suitable for studying morphological aspects of various melanin granules.

Place, publisher, year, edition, pages
2001. Vol. 14, no 6, 445-449 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-26717DOI: 10.1034/j.1600-0749.2001.140604.xLocal ID: 11311OAI: diva2:247267
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2013-02-22
In thesis
1. Melanophores: cell biophysics and sensor applications
Open this publication in new window or tab >>Melanophores: cell biophysics and sensor applications
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with studies of melanophores and melanosomes by means of a physical approach. Melanophores are pigment cells that give the black colour to many vertebrates, e.g. fishes, frogs, and reptiles. Covering large areas of the skin, these cells are approximately 0.1 mm in diameter, and they contain black pigment granules called melanosomes.

The geometry and the electric charge of isolated melanosomes were two physical properties that were studied. The electric charge was measured by electrophoresis and was found to be (-1.7 ± 0.2)·10-16 Coulomb in average. The geometry of melanosomes was measured using Scanning Force Microscopy, SFM, and resulted in an ellipsoidal shape with an average major diameter of 840 ± 20 nm.

Under nervous and hormonal control, melanophores rearrange the intracellular melanosomes from a scattered distribution, called dispersed, to a state where all melanosomes are accumulated in the cell centre, called the aggregated state. In this way, melanophores change from black towards transparent. This gives an animal the ability to change not only between being pale or dark, but also between different colours by using melanophores to cover and uncover the colours of different types of pigment cells from underlying layers.

The volume of melanosomes was measured with SFM. This study resulted in a difference of 18% when individual melanosomes from aggregated and dispersed melanophores were measured separately.

Magnetic field exposure of melanophores has been reported to affect the aggregation. However, contradicting results are presented in the literature. To clarify the possible effect of magnetic fields on melanophores, experiments by aggregating fish melanophores under exposure to strong (8 and 14 Tesla), homogenous, static magnetic fields were carried out. Both the magnetic field-induced Lorentz force on the charged melanosomes and the reorientation of the cytoskeleton were considered as possible explanations of any effects. Whenfield experiments were compared to control experiments with zero field, no difference in aggregation levels were found. However, a more irregular speed of aggregation was seen in the 8 Tesla field than in the control experiments.

A theoretical model was developed to explain switch-like responses in biological systems. A switch-like response to a graded stimulation was sometimes seen in the case of melanophores but was shown not to have a very large so-called Hill coefficient. The model is simple in its approach. It may be applied to general phenomena and is based on the assumption of a simultaneous desorption of an activator (agonist; substrate molecule; ... ) and an inactivator (antagonist, inhibitor; ... ) caused by a collision or interaction between two effector molecules (e.g. receptors or enzymes).

Melanosomes are also found in the human body and have a remarkably capacity to bind other molecules. A well-established forensic application of this is to detect (illegal) drugs that have bound to melanosomes in hair shafts. So far this application is only qualitative. This thesis includes a characterisation of the binding of flunitrazepam to melanin. Flunitrazepam is the active substance of Rohypnol, which is a sedative that is illegal in several countries and sometimes called the "date-rape-drug".

Melanophores are excellent model systems for studies of cellular phenomena. Moreover, melanophores are also interesting in sensing aspects. The change from black to transparent is a highly visible response to substances in their surroundings and has previously been the measurand in melanophore-based biosensors. The physical approach of these studies of melanophores also had the objective of evaluating new biosensor solutions.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2001. 58 p.
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 687
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-29443 (URN)14789 (Local ID)91-7373-015-7 (ISBN)14789 (Archive number)14789 (OAI)
Public defence
2001-05-11, Föreläsningssal Elsa Brändström, Universitetssjukhuset, Linköping, 09:15 (English)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-02-22

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Testorf, MartinRoback, KerstinLundström, IngemarSvensson, Samuel
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