Height Changes Associated with Pigment Aggregation inXenopus laevisMelanophores

Abstract

Melanophores are pigment cells found in the skin of lower vertebrates. The brownish-black pigment melanin is stored in organelles called melanosomes. In response to different stimuli, the cells can redistribute the melanosomes, and thereby change colour. During melanosome aggregation, a height increase has been observed in fish and frog melanophores across the cell centre. The mechanism by which the cell increases its height is unknown. Changes in cell shape can alter the electrical properties of the cell, and thereby be detected in impedance measurements. We have in earlier studies of Xenopus laevis melanophores shown that pigment aggregation can be revealed as impedance changes, and therefore we were interested in investigating the height changes associated with pigment aggregation further. Accordingly, we quantified the changes in cell height by performing vertical sectioning with confocal microscopy. In analogy with theories explaining the leading edge of migrating cells, we investigated the possibility that the elevation of plasma membrane is caused by local swelling due to influx of water through HgCl2-sensitive aquaporins. We also measured the height of the microtubule structures to assess whether they are involved in the height increase. Our results show that pigment aggregation in X. laevis melanophores resulted in a significant height increase, which was substantially larger when aggregation was induced by latrunculin than with melatonin. Moreover, the elevation of the plasma membrane did not correlate with influx of water through aquaporins or formation of new microtubules, Rather, the accumulation of granules seemed to drive the change in cell height.

Measurement and finite element modeling of the force balance in the vertical section of adhering vascular endothelial cells

“…The vertical force balance in adhering stationary cells has been explicitly discussed only by analogy with the liquid drop on a solid substrate (Boal, 2002), not considering the contribution of subcellular structural components. Thus despite considerable research on the planar force balance (Ingber, 2003;Tan et al, 2003;Deguchi et al, 2005aDeguchi et al, , 2006Kumar et al, 2006) that is predominantly regulated by the stress fiber and focal adhesions, there are few quantitative considerations on the vertical force balance (Immerstrand et al, 2005) although the vertical force balance is important for future investigation on quantitative evaluation of the force transmission in the actual cells having localized structural components.…”