Intracellular calcium dynamics during photolysis

Chondrocyte burst promotes space for mineral expansion

Analysis of tissue development from multidisciplinary approaches can result in more integrative biological findings, and can eventually allow the development of more effective bioengineering methods. In this study, we analyzed the initial steps of mineral formation during secondary ossification of mouse femur based on biological and bioengineering approaches. We first found that some chondrocytes burst near the mineralized area. External factors that could trigger chondrocyte burst were then investigated. Chondrocyte burst was shown to be modulated by mechanical and osmotic pressure. A hypotonic solution, as well as mechanical stress, significantly induced chondrocyte burst. We further hypothesized that chondrocyte burst could be associated with space-making for mineral expansion. In fact, ex vivo culture of femur epiphysis in hypotonic conditions, or under mechanical pressure, enhanced mineral formation, compared to normal culture conditions. Additionally, the effect of mechanical pressure on bone formation in vivo was investigated by immobilization of mouse lower limbs to decrease the body pressure onto the joints. The results showed that limb immobilization suppressed bone formation. Together, these results suggest chondrocyte burst as a novel fate of chondrocytes, and that manipulation of chondrocyte burst with external mechano-chemical stimuli could be an additional approach for cartilage and bone tissue engineering.

Photo-Induced Damages of Cytoplasmic and Mitochondrial Membranes by a [C60]Fullerene Malonic Acid Derivative

The biological activities of fullerene derivatives have attracted much attention in the last decade. In this paper, effects of dimalonic acid C60 (DMA C60) on cytoplasmic membrane, intracellular calcium concentration ([Ca2+]i), and mitochondrial membrane in HeLa cells were studied by using laser scanning confocal microscopy together with fluorescent probes propidium iodide (PI), fluo-3 acetoxymethyl ester (fluo-3 AM), and tetramethyl rhodamine methyl ester (TMRM). The data showed that under laser irradiation produced by a Kr/Ar laser source with a low power less than 1 mW, DMA C60 might induce damages against both cytoplasmic and mitochondrial membranes in a time- and dose-dependent manner. Prior to leakage of cytoplasmic membrane, a transient increase in [Ca2+]i occurred due to influx of calcium from the culture medium. These data provided some novel clues to explain the mechanisms involved in the photo-induced cytotoxicity of fullerene derivatives.

Light sensitivity of the ciliate Tetrahymena vorax induced by the fluorescent dye acridine orange

The ciliate Tetrahymena vorax is normally insensitive to light. However, after uptake of acridine orange, blue light evokes instant backward swimming. The dye accumulates mainly in posterior vacuoles, with half-maximal uptake after 1 min. Illumination for 10 s induced a depolarisation of approximately 15 mV lasting less than 2 s, followed by a sustained hyperpolarisation of approximately 20 mV. Deciliated cells displayed a similar response. The hyperpolarisation was linked to reduced membrane resistance, showed a reversal potential of approximately -55 mV and was blocked by 1 mmol l(-1) TEA. The rate of rise of electrically evoked Ca(2+)-spikes was reduced during the hyperpolarisation, which is compatible with elevated cytosolic Ca(2+) concentration. This suggests that the hyperpolarisation may be caused by activation of Ca(2+)-sensitive K(+) channels. The depolarisation was abolished in Ca(2+)-free medium, whereas the hyperpolarisation was unaffected. Illumination for 2 s, or prolonged stimulation restricted to the anterior part of the cell, induced depolarisation only. Illumination of the posterior part caused delayed hyperpolarisation with no preceding depolarisation. We conclude that the induced backward swimming is associated with Ca(2+) influx through anterior channels, while Ca(2+) released from intracellular stores activates K(+) channels responsible for the delayed hyperpolarisation.