Light-triggered pH banding profile in Chara cells revealed with a scanning pH microprobe and its relation to self-organization phenomena

When exposed to light, Characean cells develop a pattern of alternating alkaline and acid bands along the cell length. The bands were identified with a tip-sensitive antimony pH microelectrode positioned near one end of Chara internode at a distance of 50-100 microm from the cell wall. The stage with Chara cell was moved along its longitudinal axis at a computer-controlled speed (100 or 200 microm s(-1)) relative to the pH probe over a distance of 50 mm. Under sufficient uniform illumination of the cell (from 100 to 2.5 Wm(-2)), the homogeneous pH distribution becomes unstable and a banding pattern is formed, the spatial scale of which decreases with the light intensity. If the cell is locally illuminated, bands are formed only in the region of illumination. It is shown that the inhibition of cyclosis by cytochalasin B leads to the disappearance of the banding pattern. The addition of ammonium (weak base) inhibited the banding pattern, whereas acetate (weak acid) alleviated the inhibitory effect of ammonium and restored the pH banding. A model explaining the observed phenomena is formulated in terms of proton concentration outside and bicarbonate concentration inside the cell. It contains two diffusion equations for the corresponding ions with nonlinear boundary conditions determined by ion transport processes across the cell membrane. The model qualitatively explains most of the experimental observations. It describes the dependence of the pattern characteristics on the light intensity and reveals the role of cyclosis in this phenomenon.     

Low-power laser irradiation induces leukocyte priming

Laser radiation (LR) of various spectral composition has been broadly used in clinical practice. However, the mechanism of the stimulating effects of LR remains obscure. The effect of He-Ne LR (633 nm) on human blood leukocytes was investigated both in the absence and presence of 8.65 nmol/l phthalocyanine (PhC). Irradiation of non-stimulated leukocytes with 0.025 to 0.5 J/cm2 did not lead to any activation of their luminol-dependent chemiluminescence (LCL). On the other hand, LR increased in most cases the subsequent CL response of the cells to opsonized zymosan (priming action of He-Ne-laser light). The effect of LR on the leukocytes was not standard. In irradiated leukocytes isolated from patients with severe acute or chronic pneumonia, or chronic bronchitis, the maximal LCL exceeded that for non-irradiated cells by 80% (0.05 J/cm2), 20-25% (0.15 J/cm2), and 0%, respectively (doses are shown in parentheses). Further increase of the exposure brought about a dose-dependent inhibition of LCL in cells from patients with severe acute and chronic pneumonia. There was an intriguing relationship between maximal CL responses of leukocytes subjected to laser irradiation in the presence and without PhC. When the priming effect of LR on isolated cells was small, it increased in the presence of exogenous photosensitizer, phthalocyanine; in cells of severely ill patients where the initial effect of LR was strong, Pc inhibited the priming action of LR. Apparently, different cells contained different amounts of endogenous photosensitizer(s); the addition of exogenous sensitizer increased the priming action of LR at low concentrations and decreased it at higher concentrations of the endogenous photosensitizer.     

Interaction of tumor and normal blood cells with ethylene oxide and propylene oxide block copolymers

Ethylene oxide and propylene oxide block copolymers (pluronics) are widely known as agents that promote drug penetration across biological barriers. We have studied the interaction of normal and malignant blood cells with pluronics L61 and P85 that have different hydrophobicity. SP2/0 myeloma cells accumulated pluronics while normal cells adsorb most of the polymer on the surface. Interaction of pluronics with cells resulted in drastic changes of membrane microviscosity. Tumor cell membrane microviscosity decreased after pluronics adsorption, in contrast to normal cells, whose membrane microviscosity was enhanced. We suppose that sensitivity of tumor cell membrane microviscosity to the pluronics action correlates with its permeability for molecular substances.