PubMed · 7869578
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1994. N-methylolacrylamide.. https://pubmed.ncbi.nlm.nih.gov/7869578/
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Four types of ion-selective channels were found by the patch-clamp technique in the human erythroleukemia K562 cells. I) in cell-attached configuration at potentials less negative than -40 mV an 8 ps channel was detected. The potential dependence of channel activity suggests that this is the TTX-sensitive Na+ channel. II) A cation-selective channel was observed with equal permeability for Na+ and K+ and a potential-independent single-channel conductance of 19 pS. The channel is activated by intracellular Ca2+ and inhibited by TEA, III) A predominantly anion-selective channel was identified with the selectivity sequence NO3- > J- > Cl- = Br- >> SO4(2-). The single-channel conductance shows outward rectification, and is in symmetrical NaCl solution 19 pS at -60 mV and 54pS at +50 mV. The open- and closed-time distributions suggest one open and at least four closed states. At submicromolar concentrations, the open state is blocked by H2DIDS leading to channel flicker between open and blocked channel; higher concentrations (apparent KI = 6.8 uM) lead to a longer-lasting blocked state. Both components of inhibition are reversible. IV) In addition, an 8 pS, Na(+)- and K(+)- selective channel could be induced by application of palytoxin. For channel activity, the presence of extracellular Na+ is essential. It is assumed that the Na+, K(+)-pump molecule is involved in the channel formation. Similarly, it is discussed whether the anion-selective channel represents a pore conformation of an electrically silent anion exchanger.
We recently reported the new concept of temperature-responsive liquid chromatography using temperature-responsive poly(N-isopropylacrylamide)-modified surfaces as high-performance liquid chromatography media with aqueous mobile phases. Incorporation of hydrophobic sites is an important factor to improve the efficacy (selectivity and retention) of temperature-responsive chromatography. Toward this goal, we have synthesized semitelechelic copolymers of N-isopropylacrylamide (IPAAm) and butyl methacrylate (BMA) having reactive terminal functional groups using telomerization. The lower critical solution temperatures of the copolymers shift to lower temperatures with increasing hydrophobic BMA content in the poly(IPAAm-co-BMA) relative to that of the IPAAm homopolymer. This temperature-responsive semitelechelic copolymer was grafted to the surface of (aminopropyl)silica through the reaction of activated ester-amine coupling. The polymer-modified silica was used as a column packing material. Separation of a mixture of five steroids having various hydrophobicities was investigated. Retention of steroids on poly(IPAAm-co-BMA)-modified columns is increased with an increase in column temperature. The capacity factors for steroids on the copolymer-modified silica beads was much larger than that on homopolymer PIPAAm-modified columns. The capacity factor for testosterone at 50 degrees C was 33.8 for poly(IPAAm-co-BMA) containing 5 mol% BMA, while that for the PIPAAm homopolymer was 15.0 at the same temperature. The influence of column temperature on steroid retention behavior on copolymer-modified stationary phases was significant compared with the case of homopolymer-modified columns. Furthermore, retention times for steroids increased remarkably with increasing BMA composition. The temperature-responsive elution behavior for the steroids was strongly affected by the hydrophobicity of the grafted polymer chains on silica surfaces. Possible protein separation in temperature-responsive liquid chromatography was explored using insulin chains A and B, and beta-endorphin fragment 1-27. On IBc-3.2-modified silica column, these three peptides were successfully separated at 30 degrees C with 0.5 M NaCl aqueous solution (pH 2.1) as mobile phase. The retention times of these peptides were related to the number of hydrophobic amino acid residues in the peptides. In the proposed chromatography system, elution of target substances is controlled only by a small change in column temperature without any further modification of the aqueous mobile phase.
In this article, capillary electrophoresis of DNA fragments and polymerase chain reaction products in sieving liquid polymers is reviewed. The first part of the review is dedicated to the development of N-substituted acrylamides, which in general guarantee a greater resistance to hydrolytic attack. Among the various monomers developed, an outstanding molecule appears to be N-acryloyl aminopropanol (AAP), which combines an extreme resistance to alkaline hydrolysis (500 times greater than plain acrylamide) with a substantially higher hydrophilicity. Poly(AAP) matrices exhibit a unique behavior in DNA separations, especially at high temperatures (60 degrees C), where most other matrices fail. In separation of antisense oligonucleotides, isoelectric buffers allow very high field strengths (up to 800 V/cm) due to their extremely low conductivity, thus permitting separations on the order of a few minutes. Among such buffers, histidine (pH = pI = 7.47) and lysine (pH = pI = 9.74) appear to be the best ones. Detection of DNA point mutations is accomplished with a peculiar nonisocratic capillary zone electrophoresis (CZE), consisting of creating temporal thermal gradients, analogous to temperature-programmed gas chromatography. A unique approach is described, consisting of creating temperature gradients not with external thermostats, but with internal Joule effects produced by voltage programming (which results in temperature ramps). The review ends with some unique applications of CZE: the possibility of precise gene dosage, relying on on-line detection and quantitation of the separated peaks. Examples of such gene dosages are given, such as assessment of Down's syndrome and determination of homozygous and heterozygous states of RhD blood groups.