Different interactions between the two sides of purple membrane with atomic force microscope tip.

Atomic force microscopy (AFM) is known to be capable of measuring local surface charge density based on the DLVO model. However, it has failed to distinguish charge density difference between the extracellular and cytoplasmic sides of purple membrane (PM) in previous studies. In this paper, tapping-mode AFM with thioglycolate-modified tips was used to image PM in buffers of different salt concentrations. When imaged in 25 mM KCl buffer, the topography of membranes appeared to be of two different types, one flat and the other domelike. Such a difference was not observed in buffers of high salt concentrations. This suggests that the topography variation results from differences in electrostatic interaction between the AFM tip and the different membrane surfaces. With images of papain-digested PM and high-resolution images of membrane surface structure, we proved that the membrane surfaces with flat topography were on the extracellular side while the surfaces with domelike topography were on the cytoplasmic side. Hence, this provides a straightforward method to distinguish the two sides of PM without the requirement of high-resolution imaging. Force-distance curves clearly demonstrated the different tip-sample interactions. The force curves recorded on the extracellular side of PM were consistent with the DLVO model, so its surface charge density can be estimated well. However, the curves recorded on the cytoplasmic side had a much longer decay length, which is supposed to be relevant to the flexibility of the C-terminus of bacteriorhodopsin (bR).

[Study on synergic or antagonistic effects of different acupoint groups on vertebro-basilar insufficiency].

OBJECTIVE: To observe the synergic or antagonistic effect of needling acupoints Fengchi (GB 20) and Tianzhu (BL 10), and Jiaji C4-C6 (EX-B2) on vertebro-basilar insufficiency (VBI). METHODS: Self-control method was used and 20 cases of VBI were respectively treated with acupuncture at Fengchi (GB 20) and Tianzhu (BL 10), Jiaji (EX-B2). Their combination and the changes of vertebro-basilar artery's (VBA) systolic velocity of blood flow was detected. RESULTS: The VBA's systolic velocity of blood flow after acupuncture were increased in all the 3 groups (P < 0.05 or P < 0.01), with no significant difference among the 3 groups (P > 0.05). CONCLUSION: Acupuncture at Fengchi (GB 20) and Tianzhu (BL 10) or Jiaji (C4-C6 ) or their combination can increase VBA's systolic velocity of blood flow, improving blood supply of vertebro-basilar artery, but they have no synergic or antagonistic effects.

Preliminarily investigating the polymorphism of self-organized actin filament in vitro by atomic force microscope.

With the atomic force microscope (AFM), we preliminarily investigated the large-scale structure of actin filaments formed in low concentration protein solution (5 microg/ml) via self-organization without the presence of any F-actin dynamic interfering factors (such as phalloidin) in vitro. It was found that the G-actin could be polymerized into ordered filamentous structures with different diameter from the slimmest filament of single F-actin to giant filament in tree-like branched aggregates. The observed polymerized actin filaments, to which our most intense attention was attracted, was discretely distributed and showed obvious polymorphism distinctly different from those in the presence of phalloidin or actin binding proteins (fimbrin, gelsolin, etc.) in previous experiments. Latter structures were mainly composed of single F-actin and/or multifilaments clearly consisting of several single F-actin. The experimental results clearly demonstrated that non-interference with the F-actin intrinsic dynamics in self-organizing could lead to the polymorphism of actin filamentous structures, and further analysis implied that the disturbance of normal F-actin dynamics by many factors could prevent the emergence of structural polymorphism, more often than not, give rise to formation of specific structures instead and different interference would bring about various particular structures under certain conditions.