Rectification of the Water Permeability in COS-7 Cells at 22, 10 and 0°C

The osmotic and permeability parameters of a cell membrane are essential physico-chemical properties of a cell and particularly important with respect to cell volume changes and the regulation thereof. Here, we report the hydraulic conductivity, Lp, the non-osmotic volume, Vb, and the Arrhenius activation energy, Ea, of mammalian COS-7 cells. The ratio of Vb to the isotonic cell volume, Vc iso, was 0.29. Ea, the activation energy required for the permeation of water through the cell membrane, was 10,700, and 12,000 cal/mol under hyper- and hypotonic conditions, respectively. Average values for Lp were calculated from swell/shrink curves by using an integrated equation for Lp. The curves represented the volume changes of 358 individually measured cells, placed into solutions of nonpermeating solutes of 157 or 602 mOsm/kg (at 0, 10 or 22°C) and imaged over time. Lp estimates for all six combinations of osmolality and temperature were calculated, resulting in values of 0.11, 0.21, and 0.10 µm/min/atm for exosmotic flow and 0.79, 1.73 and 1.87 µm/min/atm for endosmotic flow (at 0, 10 and 22°C, respectively). The unexpected finding of several fold higher Lp values for endosmotic flow indicates highly asymmetric membrane permeability for water in COS-7. This phenomenon is known as rectification and has mainly been reported for plant cell, but only rarely for animal cells. Although the mechanism underlying the strong rectification found in COS-7 cells is yet unknown, it is a phenomenon of biological interest and has important practical consequences, for instance, in the development of optimal cryopreservation

Piston, Electron microscopy of whole cells in liquid with nanometer resolution

Single gold-tagged epidermal growth factor (EGF) molecules bound to cellular EGF receptors of fixed fibroblast cells were imaged in liquid with a scanning transmission electron microscope (STEM). The cells were placed in buffer solution in a microfluidic device with electron transparent windows inside the vacuum of the electron microscope. A spatial resolution of 4 nm and a pixel dwell time of 20 s were obtained. The liquid layer was sufficiently thick to contain the cells with a thickness of 7 ؎ 1 m. The experimental findings are consistent with a theoretical calculation. Liquid STEM is a unique approach for imaging single molecules in whole cells with significantly improved resolution and imaging speed over existing methods. cellular imaging ͉ molecular labels U nderstanding cellular function at a molecular level requires imaging techniques capable of imaging whole cells with a resolution sufficient to image individually tagged proteins. Electron microscopy and X-ray diffraction are traditionally used to resolve the structures of individual proteins and to image proteins distributions in cells (1). Imaging with these techniques demands extensive sample preparation to obtain, e.g., proteins crystals, stained thin sections, or frozen samples. The cells are thus not in their native liquid state. Light microscopy is used to image protein distributions via fluorescent labels on fixed cells in liquid and in live cells to investigate cellular function (2). Superresolution techniques surpass the diffraction limit in optical microscopy (3-6), but despite recent advances, these methods are still restricted to spatial resolutions Ͼ10-20 nm. Further, their optimal performance requires extended imaging times, and significant data postprocessing. The speed can only be increased at the cost of resolution. Here, we describe a direct technique for imaging whole cells in liquid that offers nanometer spatial resolution and a high imaging speed. The principle is explained in Results COS7 fibroblast cells were labeled with 10-nm gold nanoparticles conjugated with epidermal growth factor (EGF-Au). The cells were grown, labeled, and fixed directly on the silicon nitride windows. To observe molecular rearrangements in the COS7 cells, the cells were incubated for 10 min with EGF-Au followed by additional 15-min incubation in buffer. Liquid STEM images of these cells are shown in After STEM imaging, the f low cell used fo

Electron microscopy of whole cells in liquid with nanometer resolution

Single gold-tagged epidermal growth factor (EGF) molecules bound to cellular EGF receptors of fixed fibroblast cells were imaged in liquid with a scanning transmission electron microscope (STEM). The cells were placed in buffer solution in a microfluidic device with electron transparent windows inside the vacuum of the electron microscope. A spatial resolution of 4 nm and a pixel dwell time of 20 μs were obtained. The liquid layer was sufficiently thick to contain the cells with a thickness of 7 ± 1 μm. The experimental findings are consistent with a theoretical calculation. Liquid STEM is a unique approach for imaging single molecules in whole cells with significantly improved resolution and imaging speed over existing methods

Salvinorin A: A potent naturally occurring nonnitrogenous κ opioid selective agonist

Salvia divinorum, whose main active ingredient is the neoclerodane diterpene Salvinorin A, is a hallucinogenic plant in the mint family that has been used in traditional spiritual practices for its psychoactive properties by the Mazatecs of Oaxaca, Mexico. More recently, S. divinorum extracts and Salvinorin A have become more widely used in the U.S. as legal hallucinogens. We discovered that Salvinorin A potently and selectively inhibited (3)H-bremazocine binding to cloned κ opioid receptors. Salvinorin A had no significant activity against a battery of 50 receptors, transporters, and ion channels and showed a distinctive profile compared with the prototypic hallucinogen lysergic acid diethylamide. Functional studies demonstrated that Salvinorin A is a potent κ opioid agonist at cloned κ opioid receptors expressed in human embryonic kidney-293 cells and at native κ opioid receptors expressed in guinea pig brain. Importantly, Salvinorin A had no actions at the 5-HT(2A) serotonin receptor, the principal molecular target responsible for the actions of classical hallucinogens. Salvinorin A thus represents, to our knowledge, the first naturally occurring nonnitrogenous opioid-receptor subtype-selective agonist. Because Salvinorin A is a psychotomimetic selective for κ opioid receptors, κ opioid-selective antagonists may represent novel psychotherapeutic compounds for diseases manifested by perceptual distortions (e.g., schizophrenia, dementia, and bipolar disorders). Additionally, these results suggest that κ opioid receptors play a prominent role in the modulation of human perception