Membrane-delimited cell signaling complexes: Direct ion channel regulation by G Proteins

Summary Ion channels are signaling molecules and by them-selves perform no work. In this regard they are un like the usual membrane enzyme effectors for G proteins. The pathways of G protein receptor, G protein and ion channels are, therefore, purely infor mational in function. Because a single G protein may have several ion channels as effectors, the effects should be coordinated and this seems to be the case. Inhibition of Ca²⁺ current and stimulation of K⁺ currents would have a greater impact than either alone. Additional flexibility is provided by spontane ous noise in the complexes of G protein receptor, G protein, and ion channel. By having a non-zero setpoint, the range of control is extended and the responses become bi-directional.     

Identification of a nucleo-cytoplasmic ionic pathway by osmotic shock in isolated mouse liver nuclei

Summary The observation that the nuclear envelope outer mem brane contains ion channels raises the question of whether these conductances communicate between the cytosol and the nuclear envelope cisternae or between the cytosol and the cytoplasm. Failure to detect large, nonselective holes using the patch-clamp technique has led to the speculation that ion channels and nuclear pores are in fact the same. In this paper we present evidence that the ionic channel, recorded in isolated liver nuclei with the patch-clamp configura tion of “nucleus-attached,” spans the double membrane of the envelope, providing a direct contact between nucleoplasm and cytoplasm.     

Adsorption of BSA on QAE-dextran: equilibria

Equilibrium isotherms for adsorption of bovine serum albumin (BSA) on a strong-base (QAE) dextran-type ion exchanger have been determined experimentally. They were not affected by the initial concentration of BSA but were affected by pH considerably. They were correlated by the Langmuir equation when pH >/= 5.05 and by the Freundlich equation of pH 4.8, which is close to pl approximately 4.8 of BSA. The contribution of ion exchange to adsorption of BSA on the ion exchanger was determined experimentally. The maximum amounts of inorganic anion exchanged for BSA were 1% and 0.4% of the exchange capacity of the ion exchanger at pH 6.9, respectively. Since the effect of the ion exchange on the adsorption appeared small, BSA may be adsorbed mainly by electrostatic attraction when pH >/= 5.05 and by hydrophobic interaction or hydrogen bonding at pH 4.8. When NaCl coexisted in the solution, the shape of the isotherm was similar to the Langmuir isotherm, but it is shifted to the right. When the concentration of NaCl was 0.2 mol/dm(3), BsA was not adsorbed on the resin. When BSA was dissolved in pure water, the saturation capacity of BSA on HPO(4) (2-),-orm resin was about 2 times larger than that for adsorption from the solution with buffer (pH 6.9 and 8.79). The saturation capacity for adsorption of BSA in pure water on HPO(4) (2-) + H(2)O(4) (-)-from resin was much smaller than that from the solution with buffer. The isotherms for univalent Cl(-)-and H(2)PO(4) (-)-form resin was peculiar; that is, the amount of BSA adsorbed decreased with increasing the liquid-phase equilibrium concentration of BSA. (c) 1993 John Wiley & Sons, Inc.     

Construction and evaluation of a metal ion biosensor

Escherichia coli, genetically engineered with a mercury(II)-sensitive promoter and the lux genes from Vibrio fischeri, were used as microbial bioluminescent sensors for the detection of mercury. Evaluation of this genetic construction was carried out by determining the effects of various parameters on cell suspensions maintained at constant conditions in a small 100-mL vessel. The strongest light intensities and quickest induction times occurred with cells in the midexponential growth phase maintained at 28 degrees C, concentrated to 1 x 10(9) cells/mL, mixed at very fast speeds, and aerated at 2 vvm (volume of air per volume of culture per minute) during light measurement in the small vessel. The cells were sensitive to the mercuric ion in the range of 20 nM to 4 muM (4 to 800 ppb), and the total response time was on the order of 1 hour, depending on the above parameters. The cells exhibited great specificity for mercury. The cells had almost equal specificity for organic and inorganic forms of the mercuric ion and responded more weakly to the mercurous ion. A simple, inexpensive, durable miniature probe (3 mL) was constructed and operated using the optimum parameters found in the small vessel as a guide. The range of sensitivity to the mercuric ion detected in the probe was 10 nM to 4 muM when aeration was provided. (c) 1993 John Wiley & Sons, Inc.     

Carbamylcholine-induced morphological changes and spatial dynamics of [Ca2+]c in Harderian glands of guinea pigs: calcium-dependent lipid secretion and contraction of myoepithelial cells

To determine whether lipid-secreting cells have cytosolic Ca²⁺ concentration ([Ca²⁺]_c)-related secretory mechanisms, morphological changes and intracellular calcium dynamics of Harderian glands of guinea pigs stimulated by secretagogs were studied by electron microspy and Fura-2/AM digital image analysis. Control glandular cells contained large lipid vacuoles that were bordered by multi-layered membranes. Rough-surfaced endoplasmic reticulum, mitochondria, and smooth-surfaced endoplasmic reticulum may be involved in lipid vacuole formation. Myoepithelial cells surrounded alveoli. After carbamylcholine (CCh, 10^–6, 10^–5, and 10^–3 M) stimulation, lipid materials within the membranous structures were frequently discharged by an exocytotic mechanism. Conspicuous deformation of glandular cells caused by vigorous contraction of myoepithelial cells was observed in isolated alveoli after 10^–6M CCh stimulation, whereas the deformaties of glandular tissues perfused via vessels were small even after 10^–3M CCh stimulation. Connective tissue between glandular alveoli inhibited unbridled myoepithelial-cell contraction. Fura-2/AM digital imaging analysis revealed that CCh stimulation caused an increase in [Ca²⁺]_c in isolated alveoli. The morphological reactions and changes in [Ca²⁺]_c were prevented by atropine. When extracellular calcium ions were absent, enhanced extrusion of lipid vacuoles, myoepithelial-cell contraction, and a rise in [Ca²⁺]_c after CCh stimulation were not observed. Nicotine and catecholamines had no effect on the secretion or on the dynamics of [Ca²⁺]_c. It can be concluded that acetylcholine elicits exocytosis in glandular cells and contraction of the myoepithelial cells of Harderian glands, accompanied by an increase in [Ca²⁺]_c. The dynamics of [Ca²⁺]_c of the gland alveoli are mostly dependent on extracellular Ca²⁺.     

嗜盐耐盐微生物抗盐胁迫相关离子转运蛋白研究进展

离子转运蛋白在维持细胞内pH稳态、离子动态平衡等方面发挥着重要作用。钠离子转运体和钾离子转运体在嗜盐耐盐微生物中广泛存在,其"保钾排钠"机制是微生物抗盐胁迫的两大策略之一。近年来,嗜盐耐盐微生物中许多新型钠、钾离子转运体被陆续发现,如RDD蛋白、UPF0118蛋白、DUF蛋白和KimA蛋白等;Fe³⁺、Mg²⁺等其他金属离子的转运蛋白也被证实可通过影响微生物胞内相容性溶质的合成起到渗透调节的作用。本文综述了嗜盐耐盐微生物中抗盐胁迫相关的各类离子转运蛋白,分析其分子结构和工作机理,并对这些蛋白在农业方面的应用进行了展望。继续发现新的离子转运蛋白,探究抗盐胁迫相关离子转运蛋白的结构和机理,解析各转运系统的协同作用及分子调控机制,将进一步加深对嗜盐耐盐微生物抗盐胁迫调控的认识,并为盐碱地农作物的改良等提供新的思路。     

Evaluating the phototactic behavior responses of the diamondback moth,Plutella xylostella,to some different wavelength LED lights in laboratory and field

Light traps equipped with light emitting diodes (LEDs) have been applied to manage some phototactic insect pests. The diamondback moth, Plutella xylostella, is a cosmopolitan insect pest to be seriously harmful to many cruciferous plants. The present research focused on evaluating the phototactic behavior responses of the moths to several wavelengths and photon flux densities of LED lights under laboratory and field conditions. The results from the laboratory showed that the highest phototactic behavior responses of P. xylostella moths were recorded for UV (380 nm) LED light under 1.5 µmol m⁻² s⁻¹ and 2.5 µmol m⁻² s⁻¹. The moths were more attracted to light traps equipped with 4 LEDs and 6 LEDs of 380 nm, respectively, between 20:00 and 22:00 than the other groups and night times in the field. The finding from the field was consistent with the results from the laboratory. We found that the 380 nm LED light results in the strongest attraction rate of the moths by 92.4 % and the moths caught in light trap with the UV LEDs was 1.62 times more than that with a black light. These data clearly demonstrate that P. xylostella moths have a high sensitivity to 380 nm, therefore, a 380 nm LED light trap could be useful for monitoring and controlling the moths.     

Ion-selective Microelectrodes: Their Use and Importance in Modern Plant Cell Biology

The exact ion gradients across cellular membranes and their changes due to metabolic or transport processes can be best studied with the use of ion-selective microelectrodes. The last decade of research using ion-selective microelectrodes in intact cells has proven this technique to be indispensable for the investigation of a variety of physiological questions of regulatory processes, membrane transport, cellular signalling, developmental biology and plant nutrition. Their application to selected problems has led to numerous exciting observations, many of which have changed our view concerning cellular responses to environmental stimuli and in many instances have led to a new understanding of plant cell physiology. Since, with these electrodes, intracellular as well as extracellular free ion concentrations can be simultaneously detected with electrical transport parameters such as membrane potential and membrane conductance, they can be powerful tools in the hands of many plant cell biologists.     

Helical peptides with three pairs of Asp-Arg and Glu-Arg residues in different orientations and spacings.

The helix-stabilizing effects of repeating pairs of Asp-Arg and Glu-Arg residues have been characterized using a peptide system of the same design used earlier to study Glu-Lys (Marqusee, S. & Baldwin, R.L., 1987, Proc. Natl. Acad. Sci. USA 84, 8898-8902) and Asp-Lys ion pairs (Marqusee, S. & Baldwin, R.L., 1990, In Protein Folding [Gierasch, L.M. & King, J., Eds.], pp. 85-94, AAAS, Washington, D.C.). The consequences of breaking ion pair and charge-helix dipole interactions by titration to pH 2 have been compared with the results of screening these interactions with NaCl at pH 7.0 and pH 2.5. The four peptides in each set contain three pairs of acidic (A) and basic (B) residues spaced either i, i + 4 or i, i + 3 apart. In one peptide of each kind the pairwise order of residues is AB, with the charges oriented favorably to the helix macrodipole, and in the other peptide the order is BA. The results are as follows: (1) Remarkably, both Asp-Arg and Glu-Arg peptides show the same pattern of helix stabilization at pH 7.0 found earlier for Glu-Lys and Asp-Lys peptides: i + 4 AB > i + 4 BA approximately i + 3 AB > i + 3 BA. (2) The ion pairs and charge-helix dipole interactions cannot be cleanly separated, but the results suggest that both interactions make important contributions to helix stability.(ABSTRACT TRUNCATED AT 250 WORDS)