Electrical responses of the marine ciliate Euplotes vannus (Hypotrichia) to mechanical stimulation at the posterior cell end

Electrical responses upon mechanostimulation at the posterior cell end were investigated in the marine hypotrichous ciliate Euplotes vannus. A new mechanostimulator was developed to mimic stimuli that are identical with those involved in cell-cell collisions. The receptor potential hyperpolarized by 18–35 mV within 12–25 msec, reached a peak value of -62 mV with a delay of 4–9 msec after membrane deformation, and was deactivated after 50–70 msec. Cirri were stimulated to beat accelerated backward. The corresponding receptor current exerted a similar time course with a peak of 2.4 nA. The shift of the reversal potential by 57.6 mV at a tenfold increase of [K⁺] ₀ identifies potassium ions as current carriers within the development of the receptor potential. An intracellular K concentration of 355 mmol/liter was calculated for cells in a medium that was composed similar to sea-water. The mechanically activated potassium current was totally inhibited by extracellular TEA and intracellular Cs⁺, and partially inhibited by extracellular 4-AP. The total inhibition of the current by injected EGTA points to a Ca dependence of the posterior mechanosensitivity. It was confirmed by the increase of the peak current amplitude with rising [Ca²⁺] ₀ . Sodium presumably repolarizes the receptor potential because the repolarization was delayed and after-depolarizations were eliminated in media without sodium. Since deciliation did not affect mechano-sensitivity, the corresponding ion channels reside within the soma membrane.The authors wish to thank Mr. Norbert Spreckelmeier from the electronics workshop and Mr. Herbert Lutter from the fine-mechanical workshop of the department for their excellent work, Mrs. G. Key and Mr. H. Mikoleit for skillful technical assistance and for preparing the figures. This work was supported by Deutsche Forschungsgemeinschaft, SFB 171, C7.     

The Tol-Pal system of Acinetobacter baumannii is important for cell morphology,antibiotic resistance and virulence

International Microbiology - Acinetobacter baumannii is an opportunistic human pathogen that has become a global threat to healthcare institutions. This Gram-negative bacterium is one of the most...     

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM treeClusia hilariana

Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO₂ fixation rates of 28 mol m^-2 s^-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (q_N) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO₂ fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (q_A) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of q_A throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (F_v/F_m) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in F_v/F_m, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition.     

Treatment of HeLa cells with bacterial water extracts inhibits Shigella flexneri invasion

Abstract Pathogenesis mediated by Shigella flexneri requires invasion of the gastrointestinal epithelium. It has been previously shown that HeLa cells challenged with S. flexneri show alterations in their phosphotyrosine-containing protein profile. In this report, we demonstrated that bacterial water extracts (WE) abrogated the invasion of HeLa cells by S. flexneri in a dose-dependent manner. A proteinaceous component of S. flexneri was shown to be responsible for this inhibitory activity. Proteins encoded on the 140-MDa plasmid were not responsible for the observed inhibition. WE from other Gram-negative bacteria also inhibited Shigella invasion of HeLa cells. HeLa cells pretreated with WE showed changes in the profile and the intensity of phosphotyrosine-containing protein bands. These data were consistent with a surface protein component in WE which initiated aberrant host cell signaling at the membrane which may account for the inhibition of bacterial entry.     

A Mild Purification Method for Polysaccharide Binding Membrane Proteins: Phase Separation of Digitonin Extracts to Isolate the Hyaluronate Synthase fromStreptococcussp. in Active Form

A new method was developed to purify the streptococcal hyaluronate synthase in active form to electrophoretic homogeneity. The method is based on the extraction of protoplast membranes with digitonin and a phase separation into an aqueous and a detergent phase induced by addition of polyethylene glycol 6000 at 0°C. Proteins bound to hyaluronate were enriched in the aqueous phase, whereas other membrane proteins resided in the detergent phase. Final purification of the hyaluronate synthase was achieved by ion exchange chromatography.     

Qualitative mathematical discussion of different evolutionary states in water transport systems of plants

We shall present several qualitative mathematical models to describe the early evolution of water transport systems in plants. To perform this in a systematic way we apply methods which have been developed in phenomenological synergetics. These methods rest on the fact that it becomes possible to describe the macroscopic behavior of a complex system by a set of control and order parameters when they are suitably identified. Our presentation is addressed to community with interdisciplinary interests.