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Biomedical subjects

D J Nelson

Publications and source records attributed to D J Nelson.

At least 163 records · Page 9Linked to original sources
PubMed1978

Volume changes and potential artifacts of epithelial cells of frog skin following impalement with microelectrodes filled with 3 m KCl.

Cells of isolated frog skin epithelium were observed microscopically during impalement with standard microelectrodes of 5 to 20 Momega resistance, filled with 3 m KCl. Impaled cells, as well as some neighboring cells, were seen to swell 10 to 100 sec after impalement, while the negative potential recorded by the microelectrode depolarized (open circuit conditions). Apparently, osmotic swelling of small epithelial cells may be caused by diffusion of KCl from such electrodes. This conclusion is supported by calculations quoted from the literature of KCl loss from microelectrodes. Intracellular recordings from epithelia with destructed cellular membranes gave negative "pre-tip potentials" of up to mV. The potentials could be altered by electrode movement, by decreasing the ambient pH or the tip-pH and by modifying the fixed charges of the tissue chemically. It is shown that even a moderate loss of KCl, which will not result in appreciable swelling, can produce negative potentials in front of the electrode tip if the protoplasm has a high density of negative fixed charges. We suggest the use of 3 m KCl electrodes with resistances above 30 Momega if after impalement compression of intracellular material by the tip can be avoided. Where such compression cannot be avoided, it is best to fill the microelectrode with an isotonic solution which mimics the electrolyte composition of the cytosol.

Animals↗
PubMed1977

Oxypurine and 6-thiopurine nucleoside triphosphate formation in human erythrocytes.

A variety of oxypurines and 6-thiopurines could be transformed by intact erythrocytes to their nucleoside triphosphate forms when incubations were extended for up to 24 hrs. The specific nucleotide monophosphate kinases which accomplish these reactions in erythrocytes were not identified but their ability to utilize 6-thioIMP, 6-thioXMP and 6-methylthioGMP as substrates, albeit very slowly, is clearly implied by these results. S-methylation of 6-thiopurines was demonstrated in erythrocytes incubated with physiological amounts of methionine-(CH3-3H). 6-Methylthioguanosine triphosphate and 6-methylmercaptopurine riboside triphosphate were formed in micromolar amounts, probably from the corresponding thiopurine nucleotides by methyl transfer from S-adenosylmethionine.

Allopurinol↗
PubMed1977

Non-cooperative Ca(II) removal and terbium(III) substitution in carp muscle calcium binding parvalbumin.

Close coorelation of atomic absorption measurements for Ca(II) contents indicates that from pH 5.8-7.4 a twentyfold excess of EGTA1 removes but one of two Ca(II) from carp parvalbumin. Thus binding of the two Ca(II) appears to be noncooperative. The maximum in emission intensity observed at a nonintegral 1.4-1.7 equivs of added Tb(III) is shown to be due to quenching by excess Tb(III). The emission intensity at the maximum increased 40% upon dialysis to remove Tb(III) not bound in the CD or EF sites. Atomic absorption results show that both Ca(CD) and Ca(EF) of native parvalbumin are easily replaced by Tb(III). Emission of Tb(EF) is not quenched by Tb(CD), but by solution Tb(III) bound at a third site, perhaps the single water molecule bound to Tb(EF). Labeling of the single sulfhydryl group with a trifluoroacetonyl gorup yields a protein with ultraviolet circular dichroism, emission, and circularly polarized emission spectra closely similar to those of native parvalbumin.

Animals↗
PubMed1976

13C nuclear magnetic resonance study of molecular motions and conformational transitions in muscle calcium binding parvalbumins.

13C nuclear magnetic resonance is used to detect the Ca2+ ion controlled conformational transition in muscle calcium binding parvalbumin and to study its intramolecular motions. Nuclear relaxation parameters are used to evaluate the reorientation rates of the protein and some of the amino acid side chains. While peripheral residues exhibit greater motional freedom than the protein interior, an interesting finding is that significant rapid internal motion is present in the phenylalanine rings comprising the hydrophobic core of the protein.

Amino Acids↗
PubMed1976

Mechanisms of phytohaemagglutinin-P-, concanavalin-A- and kaolin-induced oedemas in the rat.

Subplantar administration of either Phytohaemagglutinin-P (PHA), Concanavalin-A (Con A) or kaolin into the rat hind paw produced a dose related oedema which was still present at 48 h. Both of the lectins were more inflammagenic than kaolin on a weight per weight basis. As a result of studies using mediator inhibitors and depletors it appears that 5HT, but not histamine, may play a role in the early phases (0.5-1.5 h) of both PHA and Con A responses. Neither mediator appears to be involved in the kaolin oedema. Kinins are also likely mediators of the inflammatory response to all three irritants and could be detected in irritant injected air blebs in the rat. Prostaglandins are unlikely to play a significant role in PHA or Con A oedema since indomethacin-induced inhibition of their synthesis has only a slight inhibitory effect on the lectin induced paw oedemas and only small amounts of prostaglandin-like material could be detected in PHA or Con A blebs. However, kaolin oedema appears to have a significant prostaglandin component since large amounts of prostaglandin-like materials were detected in kaolin blebs and also indomethacin reduced the kaolin induced paw oedema. Other mediators of the inflammatory process such as complement are likely to be involved in all three irritant induced oedemas.

Animals↗
PubMed1976

Carbon-13 magnetic resonance spectra of nucleosides and their Pd(II) complexes.

Chemical shifts occurring in carbon-13 magnetic resonance spectroscopy are utilized to assess the site of complexation of nucleosides to enPdC12 in neutral aqueous solutions. Binding occurs at N3 in cytidine, thymidine, and uridien, at N7 in 1-methylguanosine, and at N1 in guanosine. For most carbon atoms adjacent to N3 in the pyrimidine nucleosides the complexation shifts of the basic ligand are about 30% of the corresponding upfield protonation shifts. All complexes are of the form enPdL2 indicating that the ligands are unidentate and that the tendency to chelation is weak. Carbon-13 magnetic resonance spectroscopy appears to be the best method for delineating these complexes in solution. Due to the high avidity of chloride ion for Pt(II), cis dichloro Pd(II) complexes may be better models for intracellular action of the corresponding Pt(II) complexes than the Pt(II) complexes themselves.

Binding Sites↗
PubMed1975

On the ability of prostaglandin E1, and arachidonic acid to modulate experimentally induced oedema in the rat paw.

1 Prostaglandins E1 and E2 but not prostaglandin F2alpha, arachidonic acid or linolenic acid, produced slight oedema when injected into the rat hindpaw. 2 Prostaglandin E1 potentiated hindpaw oedema produced by carrageenan, kaolin, bradykinin and trypsin but not that produced by 5-hydroxytryptamine (5-HT), histamine, dextran B or compound 48/80. Carrageenan- and bradykinin-induced paw oedemas were also potentiated by prostaglandin E2. Arachidonic acid potentiated responses to carrageenan and kaolin but not responses to bradykinin, trypsin, 5-HT, histamine, dextran B or compound 48/80. Linolenic acid did not potentiate hindpaw oedema induced by carrageenan. 3 Potentiation of carrageenan-induced oedema by prostaglandin E1 was not diminished by pretreatment with indomethacin, hydrocortisone or cyproheptadine. However, arachidonic acid potentiation of carrageenan oedema was reduced by pretreatment with non-steroidal anti-inflammatory drugs but not by anti-inflammatory steroids or by paracetamol. 4 The enhancement of the response to carrageenan and kaolin by prostaglandins E1, E2 and arachidonic acid is discussed in terms of kinin mediation.

Animals↗
PubMed1974

The distribution, activity, and function of the cilia in the frog brain.

1. The distribution, activity, and function of the cilia in the brain was studied using in vitro preparations of the frog choroid plexuses and ependyma.2. Scanning electron microscopy revealed that twenty to forty cilia, about 20 mum long, project from the cells of the choroidal epithelium and ependyma into the ventricular system of the brain.3. These cilia beat at a constant frequency which ranged from 5 to 20 c/s. Ciliary activity was enhanced by ATP, cyclic AMP, theophylline, and acetylcholine, and was depressed by DNP, IAA, Ni(2+), La(3+), and Co(2+).4. Ciliary motion produced a flow of c.s.f. over the surface of the cells lining the ventricles, and in the choroid plexus this flow reduced the effective thickness of the unstirred layer adjacent to the epithelium by about 100 mum.5. These results are discussed in relation to the factors that control the frequency of ciliary beating, and the role of the cilia in the circulation of the c.s.f.

Acetylcholine↗