Biomedical subjects

M L Astion

Publications and source records attributed to M L Astion.

25 records · Page 2Linked to original sources

PubMed1989

Facilitation of voltage-gated ion channels in frog neuroglia by nerve impulses.

The functions of glial cells in the nervous system are not well defined, with the exception of myelin production by oligodendrocytes, uptake of amino-acid synaptic transmitters, and a contribution to extracellular potassium homeostasis. Neuroglia have receptors for neurotransmitters which may be involved in neuron-glia interactions. Recent studies have demonstrated voltage-gated ion channels in glial membranes. In a study of the optic nerve of the frog, small areas of the surface were examined with the loose patch-clamp method, and voltage-gated Na+ and K+ channels, presumably located in the membranes of the astrocytes forming the glia limitans, were identified. We now report that nerve impulses in the axons of the frog optic nerve transiently alter the properties of the voltage-dependent membrane channels of the surface glial cells (astrocytes), a demonstration of a new form of neuron-glia interaction.

Action Potentials↗

PubMed1989

Effects of barium and bicarbonate on glial cells of Necturus optic nerve. Studies with microelectrodes and voltage-sensitive dyes.

We have studied the effects of Ba++, a known K+ channel blocker, on the electrophysiological properties of the glial cells of Necturus optic nerve. The addition of Ba++ reversibly depolarized glial cells by 25-50 mV; the half maximal deplorization was obtained with a Ba++ concentration of approximately 0.3 mM. In the presence of Ba++, the sensitivity of the membrane to changes in K+ was reduced and there was evidence of competition between K+ and Ba++ for the K+ channel. These effects, which were accompanied by a large increase in the input resistance of the glial cells, indicate that Ba++ blocks the K+ conductance in glial cells of Necturus optic nerve. With the K+ conductance reduced, we were able to investigate the presence of other membrane conductances. We found that in the presence of Ba++, the addition of HCO3- caused a Na+-dependent hyperpolarization that was sensitive to the disulfonic stilbene SITS (4-acetamido-4'-isothiocyanostilbene-2, 2'-disulfonic acid). Removal of Na+ resulted in a HCO3- -dependent, SITS-sensitive depolarization. These results are consistent with the presence in the glial membrane of an electrogenic Na+/HCO3- cotransporter in which Na+, HCO3-, and net negative charge are transported in the same direction. In Cl- -free solutions, the Ba++-induced depolarization increased, suggesting a small permeability to Cl-. Using voltage-sensitive dyes and a photodiode array for multiple site optical recording, the distribution of potential changes in response to square pulses of intracellularly injected current were recorded before and after the addition of increased and the decay of amplitude as a function of distance decreased. Such results indicate that Ba++ increases the membrane resistance more than the resistance of the intercellular junctions.

Animals↗

PubMed1988

Electrogenic Na+/HCO3- cotransport in neuroglia.

Membrane potential recording from glial cells in Necturus optic nerve in the presence of 2 mM Ba++, which was added to block the K+ conductance, gave the following results. 1) In HCO3- -free, low-Na+ solutions (11% of control; Na+ replaced with N-methyl-D-glucamine), the hyperpolarizing effect of adding 10 mM HCO3- was reduced by approximately 80%. 2) 4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulfonic acid (SITS, 0.1 or 1 mM) reduced the effect of HCO3- by at least 50%. 3) In the presence of HCO3-, reduction of Na+ caused a depolarization which was much larger than that observed in nominally HCO3- -free solutions. These observations indicate the presence in the glial membrane of an electrogenic Na+/HCO3- cotransporter in which the stoichiometry of HCO3- to Na+ is greater than 1.

Animals↗

PubMed1988

K+ accumulation in the space between giant axon and Schwann cell in the squid Alloteuthis. Effects of changes in osmolarity.

In a train of impulses in squid giant axon, accumulation of extracellular potassium causes successive afterhyperpolarizations to be progressively less negative. In Loligo, Frankenhaeuser and Hodgkin had satisfactorily accounted for the characteristics of this effect with a model in which the axon is surrounded by a space, width theta, and a barrier of permeability P. In axons isolated from Alloteuthis, we found that the model fitted the observations quite well. Superfusing the axon with hypotonic artificial seawater (ASW) caused theta and P to decrease, and, conversely, hypertonic ASW caused them to increase: this would be the case if both the space and the pathway through the barrier were extracellular. In some cases, in normal ASW, the afterhyperpolarizations in a train decreased very little, less than 0.7 mV. In these extreme cases, theta was estimated to be 190 nm and P to be 7 x 10(-4) cm s-1, both several times the values of 30 nm and 6 x 10(-5) cm s-1 estimated by Frankenhaeuser and Hodgkin. We suggest that in vivo the periaxonal space may be considerably wider than that seen in conventionally fixed squid tissue.

Action Potentials↗

PubMed1987

Effects of bicarbonate on glial cell membrane potential in Necturus optic nerve.

Intracellular electrodes were used to continuously monitor the membrane potential of glial cells in the isolated Necturus optic nerve. Addition of up to 10 mM extracellular bicarbonate (with CO2), at constant pH, produced a hyperpolarization of up to 10 mV (with a time course almost as fast as that of a K+ depolarization) that returned toward baseline during the following 2-15 min. Upon bicarbonate withdrawal, the potential transiently became more positive. The bicarbonate effects were magnified when the K+ conductance was decreased and the cell depolarized by the addition of barium. Similar bicarbonate effects were observed in Cl- free solutions. These results suggest to us that: glial cells have a bicarbonate permeability of the same order as that to K+ and glial cells buffer transient changes in acid base balance in the neuronal microenvironment at the expense of their internal pH.

Animals↗

PubMedDate not supplied

Cytoplasmic tutor: a program for teaching interpretation of a microscope-based laboratory test.

Antibodies to cytoplasmic antigens can be identified with a microscope-based indirect immunofluorescence assay that uses a mouse stomach-kidney substrate. The antibodies are diagnostic markers in chronic active hepatitis, primary biliary cirrhosis, pernicious anemia, and other autoimmune diseases. We describe the development and features of an image-based computer program for teaching medical technologists and other health care workers the proper interpretation of cytoplasmic fluorescence staining patterns. The program, called Cytoplasmic Tutor, is written in Microsoft Visual Basic for Windows and runs on an 80486 microcomputer. it is based on a library of digital images, with key features described by overlays of text. The images were collected and processed with a computer-based fluorescence video microscopy system assembled in our laboratory.

Animals↗

PubMedDate not supplied

ANCA-Tutor: a program that teaches interpretation of an immunofluorescence assay.

The microscope-based immunofluorescence assay for anti-neutrophil cytoplasmic antibodies (ANCAs) is used in the evaluation of patients with Wegener's granulomatosis and related forms of vasculitis. We developed an interactive personal computer program, ANCA-Tutor, that introduces users to the assay and examines their understanding of the test. The program runs under Microsoft Windows and is based on processed digital images of human neutrophils stained in a standard immunofluorescence test. The images contain descriptive text overlays. The program contains a library of reference images and strategies for distinguishing between staining patterns.

Antibodies, Antineutrophil Cytoplasmic↗