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1.  Determination of the Young's modulus of the epicuticle of the smooth adhesive organs of Carausius morosus using tensile testing 
The Journal of Experimental Biology  2014;217(20):3677-3687.
Adhesive organs like arolia of insects allow these animals to climb on different substrates by creating high adhesion forces. According to the Dahlquist criterion, adhesive organs must be very soft, exhibiting an effective Young's modulus of below 100 kPa to adhere well to substrates. Such a low effective Young's modulus allows the adhesive organs to make almost direct contact with the substrate and results in van der Waals forces along with capillary forces. In previous studies, the effective Young's moduli of adhesive organs were determined using indentation tests, revealing their structure to be very soft. However, adhesive organs show a layered structure, thus the measured values comprise the effective Young's moduli of several layers of the adhesive organs. In this study, a new approach is illustrated to measure the Young's modulus of the outermost layer of the arolium, i.e. of the epicuticle, of the stick insect Carausius morosus. As a result of the epicuticle being supported by upright fibres, tensile tests allow the determination of the Young's modulus of the epicuticle with hardly influence from subjacent layers. In our tensile tests, arolia of stick insects adhering on a latex membrane were stretched by stretching the membrane while the elongation of the contact area between an arolium and the membrane was recorded. For analysis, mathematical models of the mechanical system were developed. When fed with the observed elongations, these models yield estimates for the Young's modulus of the epicuticle of approximately 100 MPa. Thus, in arolia, a very thin layer (~225 nm) of a rather stiff material, which is less susceptible to abrasion, makes contact with the substrates, whereas the inner fibrous structure of arolia is responsible for their softness.
PMCID: PMC4198382  PMID: 25214493
Finite element simulation; Cuticle; Adhesion; Stick insects; Arolium; Carausius morosus
2.  Possible roles of LI-Cadherin in the formation and maintenance of the intestinal epithelial barrier 
Tissue Barriers  2013;1(1):e23815.
LI-cadherin belongs to the so called 7D-cadherins, exceptional members of the cadherin superfamily which are characterized by seven extracellular cadherin repeats and a small cytosolic domain. Under physiological conditions LI-cadherin is expressed in the intestine and colon in human and mouse and in the rat also in hepatocytes. LI-cadherin was shown to act as a functional Ca2+-dependent adhesion molecule, linking neighboring cells and a lot of biophysical and biochemical parameters were determined in the last time. It is also known that dysregulated LI-cadherin expression can be found in a variety of diseases. Although there are several hypothesis and theoretical models concerning the function of LI-cadherin, the physiological role of LI-cadherin is still enigmatic.
PMCID: PMC3879124  PMID: 24665380
CDH17; IC; LI-cadherin; cadherin-17; enterocytes; osmoregulation
3.  The function of 7D-cadherins: a mathematical model predicts physiological importance for water transport through simple epithelia 
7D-cadherins like LI-cadherin are cell adhesion molecules and represent exceptional members of the cadherin superfamily. Although LI-cadherin was shown to act as a functional Ca2+-dependent adhesion molecule, linking neighboring cells together, and to be dysregulated in a variety of diseases, the physiological role is still enigmatic. Interestingly 7D-cadherins occur only in the lateral plasma membranes of cells from epithelia of water transporting tissues like the gut, the liver or the kidney. Furthermore LI-cadherin was shown to exhibit a highly cooperative Ca2+-dependency of the binding activity. Thus it is tempting to assume that LI-cadherin regulates the water transport through the epithelium in a passive fashion by changing its binding activity in dependence on the extracellular Ca2+.
We developed a simple mathematical model describing the epithelial lining of a lumen with a content of variable osmolarity covering an interstitium of constant osmolarity. The width of the lateral intercellular cleft was found to influence the water transport significantly. In the case of hypertonic luminal content a narrow cleft is necessary to further increase concentration of the luminal content. If the cleft is too wide, the water flux will change direction and water is transported into the lumen. Electron microscopic images show that in fact areas of the gut can be found where the lateral intercellular cleft is narrow throughout the lateral cell border whereas in other areas the lateral intercellular cleft is widened.
Our simple model clearly predicts that changes of the width of the lateral intercellular cleft can regulate the direction and efficiency of water transport through a simple epithelium. In a narrow cleft the cells can increase the concentration of osmotic active substances easily by active transport whereas if the cleft is wide, friction is reduced but the cells can hardly build up high osmotic gradients. It is now tempting to speculate that 7D-cadherins, owing to their location and their Ca2+-dependence, will adapt their binding activity and thereby the width of the lateral intercellular cleft automatically as the Ca2+-concentration is coupled to the overall electrolyte concentration in the lateral intercellular cleft. This could provide a way to regulate the water resorption in a passive manner adapting to different osmotic conditions.
PMCID: PMC3138449  PMID: 21663598
4.  Moisture harvesting and water transport through specialized micro-structures on the integument of lizards 
Several lizard species that live in arid areas have developed special abilities to collect water with their bodies' surfaces and to ingest the so collected moisture. This is called rain- or moisture-harvesting. The water can originate from air humidity, fog, dew, rain or even from humid soil. The integument (i.e., the skin plus skin derivatives such as scales) has developed features so that the water spreads and is soaked into a capillary system in between the reptiles' scales. Within this capillary system the water is transported to the mouth where it is ingested. We have investigated three different lizard species which have developed the ability for moisture harvesting independently, viz. the Australian thorny devil (Moloch horridus), the Arabian toadhead agama (Phrynocephalus arabicus) and the Texas horned lizard (Phrynosoma cornutum). All three lizards have a honeycomb like micro ornamentation on the outer surface of the scales and a complex capillary system in between the scales. By investigation of individual scales and by producing and characterising polymer replicas of the reptiles' integuments, we found that the honeycomb like structures render the surface superhydrophilic, most likely by holding a water film physically stable. Furthermore, the condensation of air humidity is improved on this surface by about 100% in comparison to unstructured surfaces. This allows the animals to collect moisture with their entire body surface. The collected water is transported into the capillary system. For Phrynosoma cornutum we found the interesting effect that, in contrast to the other two investigated species, the water flow in the capillary system is not uniform but directed to the mouth. Taken together we found that the micro ornamentation yields a superhydrophilic surface, and the semi-tubular capillaries allow for an efficient passive – and for Phrynosoma directed – transport of water.
PMCID: PMC3148043  PMID: 21977432
capillary; horned lizard; rain harvesting; thorny devil; water transport
5.  Cell-Cell Contact Formation Governs Ca2+ Signaling by TRPC4 in the Vascular Endothelium 
The Journal of Biological Chemistry  2009;285(6):4213-4223.
TRPC4 is well recognized as a prominent cation channel in the vascular endothelium, but its contribution to agonist-induced endothelial Ca2+ entry is still a matter of controversy. Here we report that the cellular targeting and Ca2+ signaling function of TRPC4 is determined by the state of cell-cell adhesions during endothelial phenotype transitions. TRPC4 surface expression in human microvascular endothelial cells (HMEC-1) increased with the formation of cell-cell contacts. Epidermal growth factor recruited TRPC4 into the plasma membrane of proliferating cells but initiated retrieval of TRPC4 from the plasma membrane in quiescent, barrier-forming cells. Epidermal growth factor-induced Ca2+ entry was strongly promoted by the formation of cell-cell contacts, and both siRNA and dominant negative knockdown experiments revealed that TRPC4 mediates stimulated Ca2+ entry exclusively in proliferating clusters that form immature cell-cell contacts. TRPC4 co-precipitated with the junctional proteins β-catenin and VE-cadherin. Analysis of cellular localization of fluorescent fusion proteins provided further evidence for recruitment of TRPC4 into junctional complexes. Analysis of TRPC4 function in the HEK293 expression system identified β-catenin as a signaling molecule that enables cell-cell contact-dependent promotion of TRPC4 function. Our results place TRPC4 as a Ca2+ entry channel that is regulated by cell-cell contact formation and interaction with β-catenin. TRPC4 is suggested to serve stimulated Ca2+ entry in a specific endothelial state during the transition from a proliferating to a quiescent phenotype. Thus, TRPC4 may adopt divergent, as yet unappreciated functions in endothelial Ca2+ homeostasis and emerges as a potential key player in endothelial phenotype switching and tuning of cellular growth factor signaling.
PMCID: PMC2823560  PMID: 19996314
Signal Transduction/Calcium; Tissue/Organ Systems/Endothelium; Adhesion; Cell-cell Interaction; TRP Channels; TRPC4; VE-cadherin; Catenin; Transient Receptor Potential Channel
6.  Investigating the Locomotion of the Sandfish in Desert Sand Using NMR-Imaging 
PLoS ONE  2008;3(10):e3309.
The sandfish (Scincus scincus) is a lizard having the remarkable ability to move through desert sand for significant distances. It is well adapted to living in loose sand by virtue of a combination of morphological and behavioural specializations. We investigated the bodyform of the sandfish using 3D-laserscanning and explored its locomotion in loose desert sand using fast nuclear magnetic resonance (NMR) imaging. The sandfish exhibits an in-plane meandering motion with a frequency of about 3 Hz and an amplitude of about half its body length accompanied by swimming-like (or trotting) movements of its limbs. No torsion of the body was observed, a movement required for a digging-behaviour. Simple calculations based on the Janssen model for granular material related to our findings on bodyform and locomotor behaviour render a local decompaction of the sand surrounding the moving sandfish very likely. Thus the sand locally behaves as a viscous fluid and not as a solid material. In this fluidised sand the sandfish is able to “swim” using its limbs.
PMCID: PMC2561000  PMID: 18836551
7.  Morphometric characterisation of wing feathers of the barn owl Tyto alba pratincola and the pigeon Columba livia 
Frontiers in Zoology  2007;4:23.
Owls are known for their silent flight. Even though there is some information available on the mechanisms that lead to a reduction of noise emission, neither the morphological basis, nor the biological mechanisms of the owl's silent flight are known. Therefore, we have initiated a systematic analysis of wing morphology in both a specialist, the barn owl, and a generalist, the pigeon. This report presents a comparison between the feathers of the barn owl and the pigeon and emphasise the specific characteristics of the owl's feathers on macroscopic and microscopic level. An understanding of the features and mechanisms underlying this silent flight might eventually be employed for aerodynamic purposes and lead to a new wing design in modern aircrafts.
A variety of different feathers (six remiges and six coverts), taken from several specimen in either species, were investigated. Quantitative analysis of digital images and scanning electron microscopy were used for a morphometric characterisation. Although both species have comparable body weights, barn owl feathers were in general larger than pigeon feathers. For both species, the depth and the area of the outer vanes of the remiges were typically smaller than those of the inner vanes. This difference was more pronounced in the barn owl than in the pigeon. Owl feathers also had lesser radiates, longer pennula, and were more translucent than pigeon feathers. The two species achieved smooth edges and regular surfaces of the vanes by different construction principles: while the angles of attachment to the rachis and the length of the barbs was nearly constant for the barn owl, these parameters varied in the pigeon. We also present a quantitative description of several characteristic features of barn owl feathers, e.g., the serrations at the leading edge of the wing, the fringes at the edges of each feather, and the velvet-like dorsal surface.
The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.
PMCID: PMC2211483  PMID: 18031576
8.  Pemphigus foliaceus IgG causes dissociation of desmoglein 1–containing junctions without blocking desmoglein 1 transinteraction 
Journal of Clinical Investigation  2005;115(11):3157-3165.
Autoantibodies against the epidermal desmosomal cadherins desmoglein 1 (Dsg1) and Dsg3 have been shown to cause severe to lethal skin blistering clinically defined as pemphigus foliaceus (PF) and pemphigus vulgaris (PV). It is unknown whether antibody-induced dissociation of keratinocytes is caused by direct inhibition of Dsg1 transinteraction or by secondary cellular responses. Here we show in an in vitro system that IgGs purified from PF patient sera caused cellular dissociation of cultured human keratinocytes as well as significant release of Dsg1-coated microbeads attached to Dsg-containing sites on the keratinocyte cellular surface. However, cell dissociation and bead release induced by PF-IgGs was not caused by direct steric hindrance of Dsg1 transinteraction, as demonstrated by single molecule atomic force measurements and by laser trapping of surface-bound Dsg1-coated microbeads. Rather, our experiments strongly indicate that PF-IgG–mediated dissociation events must involve autoantibody-triggered cellular signaling pathways, resulting in destabilization of Dsg1-based adhesive sites and desmosomes.
PMCID: PMC1242188  PMID: 16211092
9.  Intracellular Ca2+ Inhibits Smooth Muscle L-Type Ca2+ Channels by Activation of Protein Phosphatase Type 2B and by Direct Interaction with the Channel  
The Journal of General Physiology  1997;110(5):503-513.
Modulation of L-type Ca2+ channels by tonic elevation of cytoplasmic Ca2+ was investigated in intact cells and inside-out patches from human umbilical vein smooth muscle. Ba2+ was used as charge carrier, and run down of Ca2+ channel activity in inside-out patches was prevented with calpastatin plus ATP. Increasing cytoplasmic Ca2+ in intact cells by elevation of extracellular Ca2+ in the presence of the ionophore A23187 inhibited the activity of L-type Ca2+ channels in cell-attached patches. Measurement of the actual level of intracellular free Ca2+ with fura-2 revealed a 50% inhibitory concentration (IC50) of 260 nM and a Hill coefficient close to 4 for Ca2+- dependent inhibition. Ca2+-induced inhibition of Ca2+ channel activity in intact cells was due to a reduction of channel open probability and availability. Ca2+-induced inhibition was not affected by the protein kinase inhibitor H-7 (10 μM) or the cytoskeleton disruptive agent cytochalasin B (20 μM), but prevented by cyclosporin A (1 μg/ ml), an inhibitor of protein phosphatase 2B (calcineurin). Elevation of Ca2+ at the cytoplasmic side of inside-out patches inhibited Ca2+ channels with an IC50 of 2 μM and a Hill coefficient close to unity. Direct Ca2+-dependent inhibition in cell-free patches was due to a reduction of open probability, whereas availability was barely affected. Application of purified protein phosphatase 2B (12 U/ml) to the cytoplasmic side of inside-out patches at a free Ca2+ concentration of 1 μM inhibited Ca2+ channel open probability and availability. Elevation of cytoplasmic Ca2+ in the presence of PP2B, suppressed channel activity in inside-out patches with an IC50 of ∼380 nM and a Hill coefficient of ∼3; i.e., characteristics reminiscent of the Ca2+ sensitivity of Ca2+ channels in intact cells. Our results suggest that L-type Ca2+ channels of smooth muscle are controlled by two Ca2+-dependent negative feedback mechanisms. These mechanisms are based on (a) a protein phosphatase 2B-mediated dephosphorylation process, and (b) the interaction of intracellular Ca2+ with a single membrane-associated site that may reside on the channel protein itself.
PMCID: PMC2229392  PMID: 9348323
L-type Ca2+ channels; gating; protein phosphatase 2B; vascular smooth muscle; patch clamp

Results 1-9 (9)