Penetration of Mannitol into the Intracellular Space of Chlorella sorokiniana

It was found that in the alga, Chlorella sorokiniana, mannitol penetrated the plasmalemma (normally thought to be impermeable to mannitol) into the intracellular space. The rate of penetration is exponential and relatively slow, having a half-time of 6 to 12 minutes and requiring over 60 minutes for complete penetration. This penetration was demonstrated both by the Millipore filtration of cells incubated with ¹⁴C-mannitol and by centrifugation of the cells through a silicon oil layer after incubation with tritiated water and ¹⁴C-mannitol. Further, mannitol caused an inhibition of both autotrophic (on CO₂) and heterotrophic (on glucose) growth. A low rate of mannitol metabolism was demonstrated, although this rate could not support heterotrophic growth.     

Stability of Polysome-Associated mRNA in Potato Tuber Cells during Aging of Tissue Discs

The stability of polysome-associated mRNA in potato tuber discsin the early stage of aging was examined by pulse-chase labelingexperiments and the change in the translational capacity ofthe RNA was studied using a wheat germ translation system. Theincorporation of pulse-fed ³H-uridine into polysomal RNA wasnot arrested immediately after the addition of actinomycin Dto the tissue, but increased by 25% during 4 hr of chasing.The radioactivity in the polysomal RNA then decreased by only30% of the value at the 4th hr during the next 9 hr in the presenceof actinomycin D. The remaining radioactivity in the polysomalRNA was stable at least for 18 hr. The proportion of radioactivityin polyadenylated RNA to that in non-polyadenylated RNA didnot vary appreciably during the chasing period. Non-polyadenylatedRNA of high molecular weight degraded faster than that of lowmolecular weight, but polyadenylated RNA did not show such size-selectivedegradation. The translational capacity of the polysomal RNAalso decreased by about 23% within 9 hr during the period ofinhibited RNA synthesis. In vivo experiments of ¹⁴C-leucineincorporation into proteins in the absence of RNA synthesissuggested that stable polysome-associated mRNA was actuallyfunctioning in the cells. SDS-polyacrylamide gel electrophoresisof the in vitro translation products indicated that mRNA codingfor polypeptides with relatively high molecular weights turnedover slightly faster than those for low molecular weight polypeptides. ¹Present address: Department of Agricultural Chemistry, Facultyof Horticulture, Chiba University, Matsudo 271, Japan. (Received May 12, 1982; Accepted August 26, 1982)     

Mannose Feeding and Its Effect on Starch Synthesis in Developing Potato Tuber Discs

Starch synthesis and accumulation is strictly associated withthe tuberization process in potatoes. To study the role of thelevels of ortho-phosphate in controlling starch biosynthesisin tuber tissues, the effect of exogenous mannose on this metabolicprocess was studied. Mannose (10 mM) had almost no effect onthe capacity of tuber slices to uptake ^I4C-sucrose. Significantstimulation of starch synthesis, however, was evident in thepresence of mannose. These results support the role of ortho-phosphatein modifying starch synthesis via the allosteric regulationof ADPglucose pyrophosphorylase. (Received June 6, 1989; Accepted August 1, 1989)     

Penetration of furosemide into phospholipid monolayers

Summary Furosemide is a surface-active anion and it tends to displace lipid monolyaers from the surface at positive polarizations lowering their potential stability range. The efficiency of the penetration and the displacement increases with decreasing surface pressure of the monolayer. Lower capacitance at a wider potential range corresponds to higher surface pressure. Monolayers with higher capacitances are indeed more readily penetrated and displaced as demonstrated by further increase in their capacitance and increase in their proton conductance. Furosemide raises the capacitance of the monolayer in the stable region due to intercalation between the head groups thus reducing the thickness of the hydrocarbon layer. In pure PC monolayer about 10% increase in capacitance is observed in the presence of 6×10^–4 m furosemide. The effect of furosemide becomes more pronounced with increasing sphingomyelin content in the mixed monolayers. The monolayer of PE is more condensed and its capacitance is lower (1.45 F/cm²) and is stable in a wider potential range than that of PC. It is less affected by furosemide and concentrations higher than 10^–3 m are required to narrow the stability range and to increase the capacitance.     

Penetration of oxygen into bacterial colonies

Previous estimates of the depth of oxygen penetration into bacterial colonies were made after measuring actual and potential respiration rates of whole colonies, or by calculation from kinetic values determined from the growth of bacteria in liquid culture. This paper reports the use of microelectrodes to measure oxygen penetration directly. Oxygen became undetectable 25-30 microns below the surface of a 120 microns deep, 18 h colony of Bacillus cereus. The colony was grown on a nutrient-rich agar medium incubated at 30 degrees C in a water-saturated atmosphere.     

Penetration of bacteria into meat.

Bacteria are confined to the surface of meat during the logarithmic phase of growth. When proteolytic bacteria approach their maximum cell density, extracellular proteases secreted by the bacteria apparently break down the connective tissue between muscle fibers, allowing the bacteria to penetrate the meat. Non-proteolytic bacteria do not penetrate meat, even when grown in association with proteolytic species.     

Penetration of protein toxins into cells

AB toxins deliver their enzymatically active A domain to the cytosol. Some AB-toxins are able to penetrate cellular membranes from endosomes where the low pH triggers their translocation. One such toxin is diphtheria toxin and important features of its translocation mechanism have been unraveled during the last year. Other toxins depend on retrograde transport through the secretory pathway to the ER before translocation, and recent findings suggest that these toxins take advantage of the ER translocation machinery normally used for transport of cellular proteins. In addition, the intracellular targets of many of these toxins have been identified recently.     

Penetration of furosemide into phospholipid monolayers

Furosemide is a surface-active anion and it tends to displace lipid monolayers from the surface at positive polarizations lowering their potential stability range. The efficiency of the penetration and the displacement increases with decreasing surface pressure of the monolayer. Lower capacitance at a wider potential range corresponds to higher surface pressure. Monolayers with higher capacitances are indeed more readily penetrated and displaced as demonstrated by further increase in their capacitance and increase in their proton conductance. Furosemide raises the capacitance of the monolayer in the stable region due to intercalation between the head groups thus reducing the thickness of the hydrocarbon layer. In pure PC monolayer about 10% increase in capacitance is observed in the presence of 6 X 10(-4)M furosemide. The effect of furosemide becomes more pronounced with increasing sphingomyelin content in the mixed monolayers. The monolayer of PE is more condensed and its capacitance is lower (approximately 1.45 microF/cm2) and is stable in a wider potential range than that of PC. It is less affected by furosemide and concentrations higher than 10(-3) M are required to narrow the stability range and to increase the capacitance.     

Penetration of bacteria into meat.

Bacteria are confined to the surface of meat during the logarithmic phase of growth. When proteolytic bacteria approach their maximum cell density, extracellular proteases secreted by the bacteria apparently break down the connective tissue between muscle fibers, allowing the bacteria to penetrate the meat. Non-proteolytic bacteria do not penetrate meat, even when grown in association with proteolytic species.     

Sulfate Uptake and Respiration of Aging Potato Discs Modified by Malonic Acid and Ultraviolet Radiation

The time course of sulfate uptake in relation to respiration is shown for aging slices of potato, Solanum tuberosum L. cv. Russet. For comparative purposes, a time course for phosphate uptake is also shown. Malonic acid depressed both the respiratory rise and the sulfate accumulating ability of aging discs. A low dose of ultraviolet radiation given at the onset of aging reduced sulfate uptake by one-half without lowering respiration. We hypothesize that sulfate uptake is controlled by at least two mechanisms: one associated with oxidative metabolism and the other mediated by protein synthesis.     

Cysteine and Methionine Regulation of Sulfate Uptake in Potato Tuber Discs (Solanum tuberosum)

Sulfate uptake in potato tuber discs is inhibited by cysteine and methionine with an 8 h lag period. Cysteine, but not methionine, inhibition can be reversed by washing the treated discs. During the experimental period cysteine is rapidly metabolized, while methionine persists as a free amino acid. Amino acid inhibition of sulfate uptake is overcome by increasing sulfate concentration. The kinetic parameters change suggesting a loss of flexibility of the sulfate uptake system caused by sulfur amino acids.     

Penetration of keratinocyte-derived cytokines into basement membrane

Keratinocytes are known to produce a wide variety of cytokines which are believed to play a significant role in cutaneous inflammatory and immunologic reactions. Considering the array of proteolytic enzymes present in the skin and the transient nature of cytokines produced from keratinocytes, it is unclear whether cytokines released by keratinocytes cross the basement membrane and contribute to distal inflammatory and immune reactions. To investigate the ability of cytokines released from human keratinocytes to cross basement membrane, we used a two chamber culture model. Keratinocytes were plated in the upper chamber coated with a reconstituted basement membrane matrix (matrigel) on a microporous membrane. To augment cytokine production, we exposed keratinocytes to 300 J/m² UVB; 24 h later the supernatants were collected, and the levels of cytokine were measured by ELISA. IL-1α, IL-6, and TNF-α were found to be increased after UVB irradiation in the upper chamber, and significant amounts (70–80%) of each cytokine were detected in the lower chamber. Our results indicate that keratinocyte-derived cytokines are available for interactions below the basement membrane and present circumstantial evidence that the production of those cytokines from keratinocytes contributes to the elevation of circulation after the UVB exposure. J. Cell. Physiol. 171:190–195, 1997. © 1997 Wiley-Liss, Inc.     

Hexose Accumulation and Turgor-Sensitive Starch Synthesis in Discs Derived from Source versus Sink Potato Tubers

The net total uptake (sum of soluble and insoluble components)of the hexoses, D-glucose and D-fructose, into sink potato (Solanumtuberosum L.) storage parenchyma was biphasic with respect tosubstrate concentration. Analysis of radioactive products revealedthat the biphasic kinetics were composed of a linear, solublecomponent superimposed on saturating starch synthesis. In contrast,in source tuber tissue, there was negligible conversion of D-glucoseto starch and the shape of the kinetic was the result of a biphasicsoluble component. The uptake of D-fructose into source tissuewas linear with respect to substrate concentration. Uptake ofthe non-metabolizable glucose analogue, 3-oxymethyl-D-glucose(3-OMG), into both sink and source tissue, demonstrated biphasickinetics, indicating the presence of a carrier for glucose.The data demonstrate that in sink potato tubers, metabolismgreatly influences apparent uptake kinetics, the kinetics ofstarch synthesis masking the kinetics of hexose transport atthe plasmalemma. Uptake of L-glucose was linear with respectto substrate concentration, an observation consistent with thissugar not being recognized by a carrier. As in the case of sucrose, in sink tuber tissue the conversionof D-glucose and D-fructose to starch was sensitive to turgor,showing a marked optimum in external osmotica containing 300mol m^–3 mannitol. The mechanisms controlling turgor-sensitivestarch synthesis in the potato tuber would, therefore, appearto be common to all three sugars. Key words: Hexose (transport), partitioning, Solanum (source, sink tubers), starch synthesis     

Penetration of cells into Millipore diffusion chambers

Diffusion chambers enclosed by Millipore filters with nominal pore sizes of 0.10, 0.22 or 0.45 μm are penetrable by small numbers of host cells, mainly macrophages. The presence, in the chambers, of a chemotactic substance causes the influx of much larger numbers of cells than medium alone.     

Penetration of Bdellovibrio bacteriovorus into Host Cells

Electron microscopy reveals that, in Bdellovibrio infection, after the formation of a passage pore in the host cell wall, the differentiated parasite penetration pole is associated with the host protoplast. This firm contact persists throughout the parasite penetration and after this process is completed. In penetrated hosts this contact is also apparent by phase microscopy. The association between the walls of the parasite and the host at the passage pore, on the other hand, is transient. Bdellovibrio do not penetrate hosts whose protoplast and cell walls are separated by plasmolysis, or in which the membrane-wall relationship is affected by low turgor pressure. It is concluded, therefore, that for penetration to occur it is essential that the host protoplast be within reach of the parasite, so that a firm contact can be established between them. A penetration mechanism is proposed that is effected by forces generated by fluxes of water and solutes due to structural changes in the infected host envelope. These forces cause a differential expansion of the host protoplast and cell wall and their separation from each other around the entry site, while the parasite remains firmly anchored to the host protoplast. Consequently, the parasite ends up enclosed in the expanded host periplasm. The actual entry, therefore, is a passive act of the parasite.