Keratins are major components of the epithelial cytoskeleton and are believed to play a vital role for mechanical integrity at the cellular and tissue level. Keratinocytes as the main cell type of the epidermis express a differentiation-specific set of type I and type II keratins forming a stable network and are major contributors of keratinocyte mechanical properties. However, owing to compensatory keratin expression, the overall contribution of keratins to cell mechanics was difficult to examine in vivo on deletion of single keratin genes. To overcome this problem, we used keratinocytes lacking all keratins. The mechanical properties of these cells were analyzed by atomic force microscopy (AFM) and magnetic tweezers experiments. We found a strong and highly significant softening of keratin-deficient keratinocytes when analyzed by AFM on the cell body and above the nucleus. Magnetic tweezers experiments fully confirmed these results showing, in addition, high viscous contributions to magnetic bead displacement in keratin-lacking cells. Keratin loss neither affected actin or microtubule networks nor their overall protein concentration. Furthermore, depolymerization of actin preserves cell softening in the absence of keratin. On reexpression of the sole basal epidermal keratin pair K5/14, the keratin filament network was reestablished, and mechanical properties were restored almost to WT levels in both experimental setups. The data presented here demonstrate the importance of keratin filaments for mechanical resilience of keratinocytes and indicate that expression of a single keratin pair is sufficient for almost complete reconstitution of their mechanical properties.

SummaryCardiomyocytes are responsible for the permanent blood flow by coordinated heart contractions. This vital function is accomplished over a long period of time with almost the same performance, although heart properties, as its elasticity, change drastically upon aging or as a result of diseases like myocardial infarction. In this paper we have analyzed late rat embryonic heart muscle cells' morphology, sarcomere/costamere formation and force generation patterns on substrates of various elasticities ranging from ∼1 to 500 kPa, which covers physiological and pathological heart stiffnesses. Furthermore, adhesion behaviour, as well as single myofibril/sarcomere contraction patterns, was characterized with high spatial resolution in the range of physiological stiffnesses (15 kPa to 90 kPa). Here, sarcomere units generate an almost stable contraction of ∼4%. On stiffened substrates the contraction amplitude remains stable, which in turn leads to increased force levels allowing cells to adapt almost instantaneously to changing environmental stiffness. Furthermore, our data strongly indicate specific adhesion to flat substrates via both costameric and focal adhesions. The general appearance of the contractile and adhesion apparatus remains almost unaffected by substrate stiffness.

A comprehensive thermodynamic model, referred to as the mixed-solvent electrolyte (MSE) model, has been applied to calculate phase equilibria, speciation, and other thermodynamic properties of selected systems that are of interest for understanding the chemistry of salt lakes and natural waters. In particular, solubilities and chemical speciation have been analyzed for various boron-containing systems, which represent an important subset of solution chemistry for such applications. The model has been shown to reproduce the speciation, solubility, and vapor–liquid equilibrium (VLE) data in the boric acid + water system over wide ranges of temperature and concentration. Specifically, solubilities have been accurately represented in the full concentration range of the B2O3 + H2O system (xB2O3 = 0~1), which includes H3BO3. The accuracy of the model has also been demonstrated by calculating solubilities in various aqueous borate systems, i.e., MnO + B2O3 + H2O (where M = Li, Na, Ca, Mg), and their mixtures with a chloride salt or an acid (i.e., LiCl, NaCl, HCl). The model predicts the effects of chemical speciation, temperature, and concentrations of various acid, base, and salt components on the formation of competing solid phases.

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