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Biomedical subjects

R Wen

Publications and source records attributed to R Wen.

44 records · Page 3Linked to original sources
PubMed1991

A deconvolution technique for improved estimation of rapid changes in ion concentration recorded with ion-selective microelectrodes.

In biological preparations, measurements of rapid, stimulus-evoked changes in ion concentration by ion-selective microelectrodes can be distorted by the limited bandwidth of these sensors. Techniques were developed to reconstruct the actual change in ion concentration using deconvolution of the electrode's output signal and the electrode's transfer function. In the vertebrate retina, a knowledge of the actual time course of a light-evoked increase in extracellular K+ concentration was used to provide a rigorous test of a hypothesis regarding the electrical origin of a clinically important component of the electroretinogram.

Animals↗
PubMed1991

M-wave of the toad electroretinogram.

1. In the retina, two distinct, light-evoked releases of K+ have been described. One takes place in the outer plexiform layer (OPL) and is termed the "distal K+ increase." The other takes place in the inner plexiform layer (IPL) and is termed the "proximal K+ increase." Although the distal K+ increase generates the electroretinogram (ERG) b-wave, the contribution of the much larger proximal K+ increase to the ERG is less well understood. In this paper we detail our investigation of the proximal K+ increase and its contribution to the ERG. We describe an ERG component, the M-wave, which had not heretofore been observed in the diffuse-flash, vitreal ERG. 2. We studied the proximal K+ increase and the ERG M-wave in the isolated retina preparation of the toad, Bufo marinus. We used K(+)-sensitive microelectrodes, as well as conventional intra- and extracellular microelectrodes, to record K+ changes, the local (or intraretinal) ERG, the vitreal ERG, and Müller cell responses. 3. As in earlier studies of the amphibian and cat M-wave, we readily observed an M-wave in the intraretinal, or local, ERG (LERG). The M-wave we studied had characteristics similar to those of M-waves that were previously described. Specifically, we found that the M-wave was generated by a Müller cell response to the proximal K+ increase and that both the proximal K+ increase and the LERG M-wave were spatially tuned. 4. We used the aspartate receptor agonist, N-methyl-DL-aspartate (NMA), to reveal that an M-wave is present in the vitreal ERG. Researchers who previously investigated the M-wave were unable to identify an M-wave in the vitreal ERG. We found that the toad ERG M-wave was a small, positive potential that was partially obscured by the much larger b-wave and slow PIII components. 5. We observed that picrotoxin (PTX) had an excitatory effect on inner retina, as evidenced by an enhanced proximal K+ increase and an enhanced M-wave. This result indicates that it is likely that GABAergic inhibition in inner retina plays an important role in retinal processing in the toad. 6. At threshold, we found that the ERG consisted mainly of an M-wave, indicating that the amphibian threshold ERG is driven by proximal retina. This result is analogous to previous observations of the threshold ERG in cat. However, in cat, the M-wave and threshold response have been described as distinct ERG components.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

[Synthesis and cerebral vasodilating effects of tetrahydro-pyrido [1,2-a] indole derivatives].

A series of 2-substituted-6-oxo-10-[2-(N-substituted)carbamoyl]ethyl- 6,7,8,9-tetrahydro-pyrido[1,2-a]indole compounds were synthesized for studying the relation between structures and cerebrovascular activities. The structures of compounds synthesized were confirmed by means of 1HNMR, MS, IR, UV and elemental analysis. Preliminary pharmacological experiments showed that all these new compounds were effective for cerebral vasodilation. Compound I7 was the best of all. The beta-diethylaminoethylamine moiety seems to be better than beta-dimethylaminoethylamine.

Animals↗
PubMed1990

Ion-selective microelectrodes suitable for recording rapid changes in extracellular ion concentration.

A method for fabricating double-barrel, ion-selective microelectrodes with fine tips (0.5-1.5 microns) and rapid response times is described. When made into K(+)-selective microelectrodes, the electrodes respond to changes in [K+]o with a time constant of 70-95 ms. The electrical response of these electrodes to common-mode voltages can be made to have a time constant of less than 2 ms, which minimizes electrical artifacts from field potentials. The application of these microelectrodes to the measurement of rapid, transient changes in retinal [K+]o is presented.

Animals↗
PubMed1990

K(+)-evoked Müller cell depolarization generates b-wave of electroretinogram in toad retina.

We tested the hypothesis that a light-evoked increase in [K+]o produces a depolarization of the Müller cell membrane, which in turn generates the electroretinogram b-wave current. Using Bufo marinus isolated retinas and K(+)-selective microelectrodes, we recorded two distinct light-evoked increases in extracellular K+ concentration: one in the inner plexiform layer and the other near the outer plexiform layer; the "distal" K+ increase was found over only 10-microns depth and had a maximum amplitude of 0.3 mM. We also recorded the electroretinogram and the light-evoked responses of rods and Müller cells. After correction for the response time of the K(+)-selective microelectrode, the waveforms of all three of these responses were almost exactly as predicted by an earlier computer simulation of the K+/Müller cell hypothesis of the b-wave by Newman and Odette [Newman, E.A. & Odette, L.L. (1984) J. Neurophysiol. 51, 164-182]. The distal K+ increase and the b-wave varied in a similar manner as a function of stimulus irradiance. Superfusion with 0.2 mM Ba2+ attenuated both the Müller cell depolarization and the b-wave by approximately 65% but had no significant effect upon the distal K+ increase. Because Ba2+ reduces K+ conductance of Müller cells, these results are very strong support of the K+/Müller cell hypothesis of the origin of the electroretinogram b-wave; the light-evoked increase in extracellular potassium concentration still is present during superfusion with Ba2+, but the K(+)-evoked Müller cell depolarization and the b-wave are decreased in amplitude because Müller cell K+ conductance is reduced.

Animals↗
PubMed1989

Extracellular pH in the isolated retina of the toad in darkness and during illumination.

1. Extracellular pH (pHo) was measured in the isolated retina preparation of the toad, Bufo marinus, using H(+)-selective microelectrodes. During superfusion with phosphate-buffered solution (pH 7.8), which had a low buffering capacity, pHo in the inner retina was 7.0-7.2 and there was a pHo gradient throughout the distal retina and into the bathing solution. 2. The retinal acidity appears to be due in part to the combined reactions of glycolysis and ATP hydrolysis, since anoxia greatly increased the pHo gradient, while superfusion with either glucose-free pyruvate solution or strophanthidin decreased this gradient. 3. Maintained illumination evoked both an acidification in the proximal retina and an alkalinization in the distal retina. Blocking synaptic transmission to second-order neurones (1.0 mM-aspartate) decreased the acidification but had little effect on the alkalinization, consistent with the notion that the alkalinization is of receptoral origin, while the acidification is of post-receptoral origin. 4. Retinal neurones extrude a significant amount of acid via Na(+)-H+ exchange, since 2.0 mM-amiloride, a blocker of Na(+)-H+ exchange, caused a sustained alkalinization in darkness and decreased the light-evoked changes in pHo, while 1.0 mM-4-acetamido-4'-isothiocyanatostilbene-2.2'-disulphonic acid (SITS), a blocker of Cl(-)-HCO3- exchange, produced a much smaller alkalinization. 5. Switching to a bicarbonate-buffered solution having a 75 times greater buffering capacity than the phosphate-buffered solution caused retinal pHo to become less acidic and significantly decreased the amplitude of the light-evoked pHo changes. 6. Addition of 2.0 mM-acetazolamide, a carbonic anhydrase inhibitor, to the bicarbonate-buffered solution increased both the pHo gradient and the light-evoked changes in pHo. These data are consistent with the idea that carbonic anhydrase, which is concentrated in Müller (glial) cells and to a lesser extent in horizontal cells, increases the effectiveness of the bicarbonate buffer system. 7. Switching from bicarbonate-buffered to phosphate-buffered solutions attenuated the b-wave of the electroretinogram, most likely by acidifying pHo. Overall, our results emphasize the importance of the bicarbonate buffer system in buffering pHo during periods of variable acid extrusion in light and in darkness.

Animals↗
PubMed1987

Formation of lymphocyte colonies under serum-free culture conditions in normal individuals and patients with chronic lymphocytic leukemia.

This paper describes a culture system which supports the formation of B cell and some T cell colonies under serum-free conditions in peripheral blood samples of normal individuals and patients with chronic lymphocytic leukemia (CLL) of B cell type. In this system, serum is replaced by bovine serum albumin, transferrin, cholesterol, insulin and catalase or horseradish peroxidase. In addition, it is necessary to add staphylococcus protein A, mitomycin-treated T cells as feeders and phytohemagglutinin leukocyte-conditioned medium as a source of growth factors. The plating efficiency is greatly enhanced when normal cells are incubated with galactose oxidase prior to plating and when CLL cells are exposed sequentially to neuraminidase and galactose oxidase.

B-Lymphocytes↗