Plenarvorträge - DPG-Tagungen

Arbeitskreis Biologische Physik Donnerstag
AKB 41 Cell Signaling
Zeit: Donnerstag 17:00–18:00 Raum: H40
Hauptvortrag AKB 41.1 Do 17:00 H40
Identification of Sensory Transduction Chains in vivo —
•Andreas Herz and Tim Gollisch — Institute for Theoretical
Biology, Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin
Every sensation begins with the conversion of a sensory stimulus into
the response of a receptor neuron. Typically, this involves a multi-step
sequence of multiple biophysical processes that cannot all be monitored
directly. Here we present a method that makes it possible to extract their
dynamical features by comparing different stimuli that cause the same
output, the only signal to be measured. Applied to auditory receptor
cells, this novel technique reveals sub-millisecond details of mechanosensory
signal processing and yields a quantitative four-step signal transduction
model. Owing to its simplicity and generality, the method is readily
applicable to a large variety of signal-processing systems.
Hauptvortrag AKB 41.2 Do 17:30 H40
Intracellular Ca 2+ Dynamics — •Martin Falcke — Hahn Meitner
Institut, SF5, Glienicker Str. 100, 14109 Berlin
AKB 50 Poster Session ”Biological Physics”
Ca 2+ is an important messenger in living cells. Intracellular Ca 2+ dynamics
is a pattern forming system showing a rich variety of phenomena.
The transition from a regime dominated by random local events to global
events like waves and oscillations can be observed. Fluorescent dyes
allow for observation of elemental events underlying global patterns at
the same time as the global pattern itself. That opens the unique possibility
to study the built up of global events from elemental random local
events. The transition from a fluctuation dominated regime to a more
deterministic behavior is accompanied by a transition from behavior determined
by spatial discreteness to a continuous medium. As a continuous
medium, intracellular Ca 2+ dynamics shows novel phenomena like e.g. a
gap of forbidden velocities in the dispersion relation. The talk gives an
introduction to Ca 2+ dynamics and its theoretical desription.
Zeit: Freitag 10:30–13:00 Raum: B
AKB 50.1 Fr 10:30 B
Spatial discreteness and stability of reaction-diffusion systems
— •Rüdiger Thul and Martin Falcke — Hahn-Meitner Institut,
Abteilung Theorie, Glienicker Strasse 100, 14109 Berlin
We present a novel approach to the dynamics of spatially discrete
reaction-diffusion equations. The approach addresses systems with active
regions on the submicrometer length scale arranged with distances
of a few micrometers. The size of the active region is determined by the
production of the diffusing substance. The linear stability analysis reveals
that due to spatial discreteness, diffusion becomes one of the major
determinants of the stability of the reaction dynamics. We illustrate this
new approach with Ca 2+ dynamics.
AKB 50.2 Fr 10:30 B
Modelling regulatory genetic system as random boolean network
— •Viktor Kaufman — AG Drossel, Hochschulstraße 6, 64289
Darmstadt
Recent results on the dynamical behaviour of critical random boolean
networks (RBN) have superseded those obtained more than 30 years ago.
There is now evidence that the mean attractor number and length grow
exponentially with the network size. This work contributes to the understanding
of those findings by means of examining the size and topology
of the relevant part of the network, using analytical arguments and computer
simulations.
AKB 50.3 Fr 10:30 B
Elektrische Stimulation von neuronalen Netzwerken über ein
strukturiertes Elektrodeninterface — •A. Reiher 1 , A. Krtschil 1 ,
S. Günther 1 , H. Witte 1 , A. Krost 1 , A. de Lima 2 , T. Opitz 2 ,
T. Voigt 2 , K. Kube 3 , V. Spravedlyvyy 3 , A. Herzog 3 und B.
Michaelis 3 — 1 Institut für Experimentelle Physik, OvG-Universität
Magdeburg — 2 Institut für Physiologie, OvG-Universität Magdeburg —
3 Institut für Elektronik, Signalverarbeitung und Kommunikationstechnik
(IESK), OvG-Universität Magdeburg, PF 4120, 39016 Magdeburg
Es ist bekannt, dass Nervenzellen aus dem Cortex von embryonalen
Ratten in vitro komplexe, neuronale Netzwerke ausbilden. Für dieses
System wurde ein in die Kultur integriertes Interface entwickelt, um eine
Kommunikation mit den Neuronen zu ermöglichen.
Dieses besteht aus einer planaren Fingerstruktur von Mikro-Gold-
Elektroden auf einer Titanhaftschicht, über die eine elektrische Stimulation
von Nervenzellen, d.h. eine induzierte Generation von Aktionspotenzialen,
realisiert wird. Um Aussagen über die erforderlichen Grössen
der Anregungen zu erhalten, wurden elektrische Stimuli systematisch hinsichtlich
Pulsdauer, -höhe und -anzahl variiert. Die Analyse der stimulierten
Netzwerkaktivität er-folgte global mit Ca 2+ -Fluoreszenz-Aufnahmen
bzw. lokal durch Patch-Clamp-Messungen. Parallel dazu wurde der Neu-
ronenresponse über das Elektrodenarray elektrisch ausgelesen. Der Einfluss
der einzelnen Stimulationsparameter auf die Netzwerkaktivität wird
im Detail vorgestellt und mit den Ergebnissen von Simulationsrechnungen
an biologisch realistischen neuronalen Netzwerken verglichen.
AKB 50.4 Fr 10:30 B
Modelling long-term evolution of food webs — •Satoshi Uchida
and Barbara Drossel — Institut für Festkörperphysik, TU Darmstadt,
Hochschulstr. 6, D-64289 Darmstadt, Germany
The relation between the stability and complexity of ecosystems is
much debated in the recent literature. An important theoretical approach
to this issue consists in exploring mathematical models of food webs,
which are networks constructed by prey-predator relationships in ecosystems.
Using computer simulations, we study a model that does not only
include Lotka-Volterra type population dynamics, but also a long-term
change in the linkage pattern and composition of the foodweb due to
species invasions and evolutionary change. We find that the foodweb becomes
unstable and collapses after some time. We explain this finding and
propose modified (and more realistic) population dynamics, for which the
complex foodweb structure persists in time.
AKB 50.5 Fr 10:30 B
Elasticity of Two-Dimensional Stiff Polymer Networks —
•Claus Heussinger and Erwin Frey — Hahn-Meitner Institut,
Berlin
We study the elasticity of two-dimensional networks of semiflexible
polymers (”Mikado model”). The essential features incorporated into the
model are the random geometry of the network and the anisotropic elasticity
of its constituents.
In a first study, the elements are modeled as purely mechanical Euler
beams [1,2]. We show that there are three distinct scaling regimes,
characterized by two characteristic length scales. In addition to a critical
rigidity percolation region and a homogeneous elastic regime (dominated
by beam compression) we find a novel intermediate scaling regime, where
the elasticity of the network is dominated by bending deformations. The
observations for the shear modulus can be rationalized by a crossover
scaling ansatz that permits to collapse the data over eight orders of magnitude
in the scaling variable.
In a second step, effective elastic properties of semiflexible polymers
are implemented to study the entropic contributions to the polymer compliance
and its effects on the scaling behaviour.
To get further insight into the nature of the force propagation, more
complicated modes of deformation can be explored. As an example, we
visualize force chains induced by the action of a microrheological probe.
[1] J. Wilhelm and E. Frey PRL 91, 108103 (2003)
[2] E. Frey, K. Kroy, J. Wilhelm and E. Sackmann, in Dynamical Net-