Revisiting the internal absorption coefficient of the retinal pigment epithelium melanosome

Randolph D. Glickman; Steven L. Jacques; Rebecca M. Hall; Neeru Kumar

doi:10.1117/12.434697

9 July 2001 Revisiting the internal absorption coefficient of the retinal pigment epithelium melanosome

Randolph D. Glickman, Steven L. Jacques, Rebecca M. Hall, Neeru Kumar

Proceedings Volume 4257, Laser-Tissue Interaction XII: Photochemical, Photothermal, and Photomechanical; (2001) https://doi.org/10.1117/12.434697
Event: BiOS 2001 The International Symposium on Biomedical Optics, 2001, San Jose, CA, United States

Abstract

Retinal pigment epithelial (RPE) cells of the vertebrate eye contain melanin packaged in structures called melanosomes. Previously, we reported that the bovine melanosome has a laser photodisruption threshold of 153.6 mJ/cm² at 25°C and 532 nm, and an internal absorption coefficient of 2237 cm^-1. Those values used an estimate of melanosome density inferred from studies of skin laser effects. We now revisit that calculation using a density value obtained from density centrifugation analysis of bovine and baboon RPE melanosomes. Stepped-density gradients (60% to 80%) of the nonionic medium, Nycodenz, were formed, and samples of melanosomes were spun on the gradients in a swinging-bucket rotor at 10,000 rpm for 60 m. Bovine melanosomes formed two populations, one at the interface between 70% and 75%, and the other between 75% and 80%, corresponding to the densities of ~1.38 and ~1.41 gm/cm³, respectively. Baboon melanosomes migrated to within the same density region. Using a density value of 1.41 gm/cm³, and assuming a water content of 52% for hydrated melanosomes, the internal absorption coefficient was calculated as 2339 cm^-1. Although this calculation uses an objective density measurement, the water content remains an estimate, and the actual value in situ may differ.

Citation Download Citation

Randolph D. Glickman, Steven L. Jacques, Rebecca M. Hall, and Neeru Kumar "Revisiting the internal absorption coefficient of the retinal pigment epithelium melanosome", Proc. SPIE 4257, Laser-Tissue Interaction XII: Photochemical, Photothermal, and Photomechanical, (9 July 2001); https://doi.org/10.1117/12.434697

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