Photoexcited chemical wave in the ruthenium-catalyzed Belousov-Zhabotinsky reaction.

The excitation of the photosensitive Belousov-Zhabotinsky (BZ) reaction induced by light stimulation was systematically investigated. A stepwise increase in the light intensity induced the excitation, whereas a stepwise decrease did not induce the excitation. The threshold values for the excitation were found to be a function of the initial and final light intensities, time variation in light intensity, and the concentration of NaBrO(3). The experimental results were qualitatively reproduced by a theoretical calculation based on a three-variable Oregonator model modified for the photosensitive BZ reaction. These results suggest that although the steady light irradiation is known to inhibit oscillation and chemical waves in the BZ system under almost all conditions, the stepwise increase in the light irradiation leads to the rapid production of an activator, resulting in the photoexcitation.

Wave propagation in the photosensitive Belousov-Zhabotinsky reaction across an asymmetric gap.

The photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated at an asymmetrically illuminated gap, which was drawn using computer software and then projected on a filter paper soaked with BZ solution using a liquid-crystal projector. The probability of the chemical wave passing through the gap with asymmetric illumination was different from that through its mirror image. The location at which the wave disappeared and the time delay of the chemical wave passing through the gap changed depending on the velocity of chemical wave propagation. The experimental results were qualitatively reproduced by a theoretical calculation based on the three-variable Oregonator model that included photosensitivity. These results suggest that the photosensitive BZ reaction may be useful for studying spatiotemporal development that depends on the geometry of excitable fields.

Role of cytokines and proteases in murine scleroderma.

Scleroderma is a fibrotic condition characterized by immunological abnormalities, vascular injury and increased accumulation of extracellular matrix proteins in the skin. Although the etiology of scleroderma has not been fully elucidated, a growing body of evidence suggests that the overproduction of extracellular matrix proteins by activated fibroblasts results from an imbalance between synthesis and degradation of connective tissues. A number of mediators, cytokines, chemokines and growth factors secreted by inflammatory cells and mesenchymal cells (fibroblasts and myofibroblasts) play an important role in the fibrotic process of scleroderma. In this article, we describe recent advances concerning immunological aspects in the pathogenesis of bleomycin-induced murine scleroderma, laying stress on the involvement of interleukin-13 (IL-13) and plasminogen activator inhibitor-1 (PAI-1).

Characteristic features in the collision of chemical waves depending on the aspect ratio of a rectangular field.

The photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated on a double rectangular field composed of two rectangular routes, which was drawn using computer software and then projected using a liquid-crystal projector on a filter paper soaked with BZ solution. When two chemical waves were generated on the rectangular routes as the initial condition, the nature of the collision of the waves could be theoretically classified into four categories depending on the initial phase difference between the two waves and the aspect ratio of the rectangular routes. The experimental results were consistent with the features of the theoretical prediction. These results suggest that the feature of wave propagation characteristically develops depending on the geometry of the excitable fields.

Upregulation of interleukin-13 and its receptor in a murine model of bleomycin-induced scleroderma.

BACKGROUND: Interleukin-13 (IL-13) has been implicated in the pathogenesis of fibrotic conditions. Previously, a murine model for scleroderma has been established by repeated local injections of bleomycin. This animal model enabled us to study local expression and production of IL-13 in skin lesions during disease progression. METHODS: Dermal sclerosis (DSc) was induced by repeated subcutaneous injections of bleomycin (1 mg/ml) in C3H/HeJ mice. IL-13 and IL-4 expressions were examined by RT-PCR, ELISA and immunohistochemistry. RESULTS: RT-PCR showed that both IL-4 and IL-13 mRNA levels in skin lesions were increased and peaked after 4 weeks of bleomycin treatment. Quantification by densitometry revealed up to 4.2- and 1.9-fold increases, respectively. Immunohistochemical localization showed in skin lesions expression of IL-13 on infiltrating inflammatory cells, including mononuclear cells and possibly mast cells, increased with DSc progression. IL-13 protein production was also significantly increased. In skin lesions, IL-13 receptor (IL-13R) alpha2 expression was augmented mainly in the infiltrating mononuclear cells after 4 weeks of bleomycin exposure. IL-13Ralpha2, but not IL-13Ralpha1, mRNA was upregulated in the whole skin after 4 weeks. On the contrary, mRNA expression of IL-13Ralpha1 and IL- 13Ralpha2 was significantly altered in the cultured fibroblasts derived from bleomycin-treated skin. CONCLUSION: These data demonstrate that in skin lesions levels of IL-13 as well as its receptor increase in parallel with DSc progression, suggesting that IL-13 promotes the progression of cutaneous fibrosis/sclerosis in the murine model of bleomycin-induced scleroderma.