Biology Reference
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displacement. It also plays a particularly important role in determining
the shape and the mechanical properties of the cell. The cytoskeleton is
essentially composed of actin, tubulin and intermediate ilaments. In the year
2000, Rotsch and Radmacher
22
monitored the evolution of cellular stiffness
after a drug-induced disruption of the cytoskeleton. Disruption of the actin
cytoskeleton, which is located peripherally, resulted in a marked decrease
in the average elastic modulus of the cell. On the other hand, disruption of
the microtubules, which are located less peripherally, elicited no measurable
change in cellular elasticity. More recent studies have revealed that even
the more deeply located tubulin cytoskeleton can be monitored by AFM.
Information concerning its stiffness is contained within the last portions of
the FD curves.
23
The effect of hormones on cellular stiffness has also been addressed in
several studies. Oberleithner
have measured the effects of the blood
pressure-regulating hormone aldosterone on vascular endothelial cells.
24,25
This drug was found to increase the stiffness of the cells by sodium uptake-
induced swelling.
26
Numerous AFM studies have provided evidence that changes in the
mechanical properties of cells are correlated with their age, the stage of
the cell cycle and the degree of differentiation. For example, the elasticity
of human umbilical vein endothelial cells increase with age,
27
whilst the
cardiomyocytes of young rats are softer (Young's modulus: 35 kPa) than
those of older (Young's modulus: 42 kPa).
28
Collinsworth
et al.
et al.
29
have shown
the Young's modulus to increase during the differentiation of myoblasts (11
kPa) into myocytes (45 kPa). In most instances, changes in the mechanical
properties of the cells relect a reorganization of the cytoskeleton, especially
of the actin and myosin components.
Another interesting ield of research that has been pursued by AFM
imaging is the inluence of pathology on the mechanical properties of cells.
Since any biochemical or structural modiication is likely to induce a change
in the mechanical properties of a cell, this ield of study could potentially
lead to the development of novel diagnostic tools. Several cell types and
diseases have been explored, and signiicant changes in the mechanical
properties have been observed. Dulinska
et al.
16
have measured the Young's
modulus for erythrocytes that were derived from patients suffering from
spherocytosis, thalassaemia or G6PD deiciency. In all of these pathologies,
the erythrocytes were found to be stiffer than their normal counterparts. The
erythrocytes that had been derived from patients with a G6DP deiciency
were the stiffest (Young's modulus: 90 kPa vs. 26 kPa [control]). Similarly,
the erythrocytes of diabetic patients have been found to be stiffer than their
normal counterparts.
30
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