External control of oscillatory glycolysis in yeast extract has been performed by application of either homogeneous temperature oscillations or stationary, spatial temperature gradients. Entrainment of the glycolytic oscillations by the 1/2- and 1/3-harmonic, as well as the fundamental input frequency, could be observed. From the phase response curve to a single temperature pulse, a distinct sensitivity of NADH-oxidizing processes, compared with NAD-reducing processes, is visible. Determination of glycolytic intermediates shows that the feedback-regulated phosphofructokinase as well as the glyceraldehyde-3-phosphate dehydrogenase are the most temperature-sensitive steps of glycolysis. We also find strong concentration changes in ATP and AMP at varying temperatures and, accordingly, in the energy charge. Construction of a feedback loop for spatial control of temperature by means of a Peltier element allowed us to apply a temperature gradient to the yeast extract. With this setup it is possible to initiate traveling waves and to control the wave velocity.

During the glycolytic degradation of sugar in a thin layer of yeast extract, travelling waves of NADH and protons can be generated that carry a state of high enzymatic activity through the system. The controlled initiation of such waves with an activator of the enzyme phosphofructokinase (PFK) and the inÑuence of various salts and co-factors on the propagation dynamics are investigated. Furthermore a Ðrst study of the dispersion of waves is presented. The experimental characterisation of this in vitro system contributes to unravelling the possible role of glycolysis for biological information processing. In this context, the provision of chemically available energy in the absence of compartmentation by glycolysis is of primary importance.

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Unipolar source drain voltage pulses of GaN/AlGaN-High Electron Mobility Transistors (HEMT) were used for stimulation of cultured neuronal networks obtained from embryonic rat cerebral cortex. The HEMT sensor was grown by metal organic vapour phase epitaxy on 2 inch sapphire substrate consisting of 10 single HEMTs concentrically arranged around the wafer center. Electrolytic reactions between the HEMT sensor surface and the culture medium were not detected by using cyclic voltammetry. During voltage pulses and resulting neuronal excitation, capacitances were recharged giving indications of the contributions of the AlGaN and the AlOx isolation layers between the two dimensional electron gas (2DEG) channel and the neuron culture. The resulting threshold current for stimulation of neuron activity strongly depends on the culture and HEMT position on the sensor surface under consideration which is caused by different impedances of each neuron culture and position within the culture. The differences of culture impedances can be explained by variations of composition, thickness, and conductivity of the culture areas.

The metabolic dynamics of yeast cells is controlled by electric pulses delivered through a spatially extended yeast cell/Au electrode interface. Concomitant with voltage pulses, oxygen is generated electrolytically at the electrode surface and delivered to the cells. The generation of oxygen was investigated in dependence of the applied voltage, width of the voltage pulses and temperature of the electrolytic solution. The local oxygen pulses at the electrodes lead to a transient activation of the aerobic energy metabolism of the yeast cells causing a perturbation in their energy balance. The effect of these local perturbations on the temporal dynamics of glycolysis in yeast cells is quantified in dependence of the energy state of cells.