Influence of an external electric field on cAMP wave patterns in aggregating Dictyostelium discoideum

Convective instability and boundary driven oscillations in a reaction-diffusion-advection model

In a reaction-diffusion-advection system, with a convectively unstable regime, a perturbation creates a wave train that is advected downstream and eventually leaves the system. We show that the convective instability coexists with a local absolute instability when a fixed boundary condition upstream is imposed. This boundary induced instability acts as a continuous wave source, creating a local periodic excitation near the boundary, which initiates waves travelling both up and downstream. To confirm this, we performed analytical analysis and numerical simulations of a modified Martiel-Goldbeter reaction-diffusion model with the addition of an advection term. We provide a quantitative description of the wave packet appearing in the convectively unstable regime, which we found to be in excellent agreement with the numerical simulations. We characterize this new instability and show that in the limit of high advection speed, it is suppressed. This type of instability can be expected for reaction-diffusion systems that present both a convective instability and an excitable regime. In particular, it can be relevant to understand the signaling mechanism of the social amoeba Dictyostelium discoideum that may experience fluid flows in its natural habitat.

The emergence of wave emitting centres in an excitable medium

The response of an excitable biological medium to a double local stimulus is considered within the context of a mathematical model for a layer of starving cells of Dictyostelium discoideum, with both spatially one- and two-dimensional (1D and 2D) system being investigated. In contrast to the response usually seen in excitable media, whereby each superthreshold stimulus delivered to the relaxed medium results in the initiation of just one travelling wave, a source emitting a sequence of waves can develop in the present excitable medium after the second stimulus. In a 1D system, only transient wave sources forming a limited number of waves are found. In 2D systems, a permanent wave sources consisting in a pair of spirals are observed as well as the transient wave sources forming circular wave patterns. The general features of the medium dynamics that underlie the observed responses to the double stimulus are discussed.

Control of wave propagation in a biological excitable medium by an external electric field

We present an experimental evidence of effects of external electric fields (EFs) on the velocity of pulse waves propagating in a biological excitable medium. The excitable medium used is formed by a layer of starving cells of Dictyostelium discoideum through which the waves of increased concentration of cAMP propagate by reaction-diffusion mechanism. External dc EFs of low intensities (up to 5 V/cm) are shown to speed up the propagation of cAMP waves towards the positive electrode and slow it down towards the negative electrode. Electric fields were also found to support an emergence of new centers, emitting cAMP waves, in front of cAMP waves propagating towards the negative electrode.

Synchronization of electrically induced calcium firings in self-assembled cardiac cells

We study the adaptive changes of a population of cells responding to external stimulus. Two-dimensionally distributed cardiac cells were homogeneously subjected to periodic electrical stimulus and intracellular calcium concentration ([Ca(2+)](i)) changes were simultaneously observed. In the absence of stimulation, coupled cells in monolayer formed groups of several cells oscillating in similar phase, while isolated cells showed irregular periodicity. In both systems, [Ca(2+)](i) oscillations were modulated by periodic stimulation, and ascending degrees of synchronization among [Ca(2+)](i) oscillations were shown as stimulation intensity increased. In a population of coupled cells, the cells act like a single robust oscillator. These results are evaluated using statistical calculations, comparing the response manner of isolated cells.