Biomedical subjects

C L Bowman

Publications and source records attributed to C L Bowman.

7 recordsLinked to original sources

PubMed1992

Mechanotransducing ion channels in astrocytes.

Ion channels present on the soma of neonatal rat astrocytes in primary cell culture were studied using the single channel recording technique. Ion channels were activated by changing the pressure in the back of the pipette. The morphological structure of the patch membrane was examined while recording channel activity. One class of channel was activated by increasing the pipette pressure (curvature-sensitive or CS channels). CS channels were observed in 150 mM KCl, 150 mM NaCl, or 150 mM sodium gluconate. At constant pressure the closed times decreased with depolarization. CS channels had a conductance of 50 pS in 150 mM NaCl, and displayed an inwardly rectifying current-voltage relationship. CS channel activity was found only in cell-attached patches, and were active only when the patch membrane curved towards the soma. The other class of channel was found to be activated by both suction and pressure (stretch-activated or SA channels). Four SA conductance levels were found: 360, 230, 144, and 70 pS in 150 mM KCl. Each conductance displayed a linear current-voltage relationship. At negative membrane potentials SA channels were inhibited by Cs+, Ba2+ or Na+. The relationship between average mechanosensory current and pressure was biphasic for SA channels and monophasic for CS channels. Combinations of SA and CS channels could be observed in the same patch. We propose that CS channels are non-specific cation channels which sense membrane tension only when the patch membrane is in a specific, permissive curvature. SA channels appear to be K(+)-selective channels that sense membrane tension independent of the direction of curvature.

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PubMed1992

Co-cultures of microglia and astrocytes from kainic acid-lesioned adult rat hippocampus: effects of glutamate.

The long-standing question concerning the direct actions of glutamate on the membrane potential of astroglial cells in the central nervous system was addressed using the in vitro kainic acid-lesioned hippocampal slice preparation and primary cell co-cultures of astrocytes and microglia derived from such lesions. The ultrastructure of the lesioned hippocampus was examined to aid in the identification of the cells appearing in culture. In culture, microglia appeared as flat cells, less than 1 micron in thickness at the edge of the cell, but thicker (about 5 microns) near the nucleus. The cytoplasm was packed with granular inclusions. Microglia appeared in two morphological forms, amoeboid and ramified. The amoeboid form was characterized by a cell body with a single process, and was always observed 1 day after starting the cell culture. Such cells became less frequent after 1 week in culture. The ramified form appeared as a rounded cell, devoid of processes, and were frequently observed in older cultures (greater than 1 week). Microglia did not round up after exposure to dibutyrylcyclic adenosine monophosphate (cAMP), and did not stain for glial fibrillary acidic protein (GFAP). An ultrastructural examination of the lesion demonstrated that microglia were present and that they contained many cytoplasmic granules similar to lipofuscin-containing granules. No filaments were observed in the cytoplasm of microglia. By contrast, the cytoplasm of astrocytes in culture had far fewer granules, rounded up to dibutyryl-cAMP, exhibited multiple processes, and stained for GFAP. In slices, astrocytes had no lipofuscin-containing granules, but numerous cytoplasmic filaments were present.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1992

Myosin light chain kinase is expressed in neurons and glia: immunoblotting and immunocytochemical studies.

The contractile protein myosin is thought to subserve motility-related functions in a wide range of eukaryotic non-muscle cells including both neurons and glia. To determine if the Ca2+/calmodulin-dependent enzyme, myosin light chain kinase (MLCK) is involved in the regulation of neural myosin we investigated the presence and localization of MLCK in a variety of neural tissues by immunoblotting and immunocytochemistry. A specific immunoreactive protein (M(r) = 146,000) was detected in blotted homogenates from many regions of rat brain and from primary cultures of either astrocytes or cerebellar granule cells grown in the absence of other cell types. At the light microscopic level, MLCK-immunoreactivity was evident in many regions of rat brain, as well as in the cultured astrocytes and cerebellar granule cells. MLCK-immunoreactivity was observed to be largely cytosolic in astrocytes but with a proportion associated with the cytoskeleton. In the cerebellar granule cells immunoreactivity was present in neuronal processes as well as somata. The detection of MLCK in neural cells suggests that MLCK-catalyzed myosin phosphorylation may couple changes in intracellular calcium concentrations to motility-related functions of neurons and glia.

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PubMed1987

Pharmacological properties of the norepinephrine-induced depolarization of astrocytes in primary culture: evidence for the involvement of an alpha 1-adrenergic receptor.

The membrane potentials of astrocytes in primary cultures prepared from neonatal rat cerebral cortices were depolarized by (-)-norepinephrine. The average first response to 10(-5) M (-)-norepinephrine was 24 mV from an average resting potential of -68 mV, and the average for the second response was 14 mV. Thus this process showed marked desensitization. The response was attributed to an activation of an alpha 1-receptor since it was about 1000 times more sensitive to inhibition by prazosin than to yohimbine or idazoxan. In addition, depolarization was seen to the application of 10(-5) M phenylephrine.

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PubMed1987

Patch clamping the outer mitochondrial membrane.

Intact giant mitochondria isolated from the liver of mice fed a diet containing cuprizone were studied using patch microelectrodes. The current-voltage curves were nonlinear, suggesting the presence of voltage-sensitive channels. In the negative range of voltage, the channels appear to close with increasing magnitude of the voltage. The dependence of the conductance on voltage is similar to that of the outer membrane channels (VDAC) studied in planar bilayers. Occasionally, over a narrow range of positive potentials, the conductance also decreases as in the bilayer studies. However, more frequently the conductance increases sharply in a completely reversible manner at potentials greater than 10 to 20 mV. The increase in conductance with voltage may be interpreted as a major rearrangement of membrane components. Qualitatively comparable results were obtained using fused outer membranes isolated from Neurospora mitochondria. The behavior of VDAC is affected by treatment with succinic anhydride or the polyanion, polymethacrylate, maleate, styrene (1:2:3). We have found similar effects in the negative range of potentials in patches from giant mitochondria treated in the same fashion.

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PubMed1986

Anion transport in astrocytes.

We have examined the question of anion-transport systems in glia using primary astrocyte cultures prepared from neonatal rat brains. These studies show that these cells have exchange or cotransport systems for Cl- that appear to be electrically neutral, that is, SITS-sensitive Cl-/Cl- or Cl-/HCO3- anion exchange, and furosemide- and bumetanide-sensitive Na+ + K+ + 2Cl- cotransport. These inhibitors inhibit a major component of the total 36Cl- flux and the remaining Cl- flux may be conductive; however, this conductive flux makes a small contribution to Em relative to K+, since large changes in [Cl-]o do not usually affect Em, which is predominantly a K+ diffusion potential. We have also found an alpha-receptor-mediated depolarization that is affected by imposed changes in Ecl. The alpha-receptor-mediated depolarization seen at normal [Cl-]o could be partially due to increased Cl- conductance because [Cl-]i appears to be several-fold higher than it would be if it were in equilibrium with the membrane potential.

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PubMed1976

Osmotic behavior and permeability of osmotically lysed mitochondria.

Experiments were carried out with water-treated isolated rat liver mitochondria (mitochondria ghosts) previously studied by Caplan and Greenawalt (Caplan, A.I., and J.W. Greenawalt. 1966. J. Cell Biol. 31:455-472) and Vasington and Greenawalt (Vasington, F., and J. Greenawalt. 1968. J. Cell Biol. 39:661-675). The ghosts have permeability properties and osmotic behavior comparable to those of isolated mitochondria. Although they have lost most of their internal contents, they must have resealed. Four properties were found which have not been previously described in systems derived from biological membranes: (a) an osmotic behavior in the virtual absence of internal components. (b) a self-arranging property in the formation of invaginations corresponding in morphology to the cristae. The results suggest that the assembly of the molecular components of the inner membrane is sufficient to specify the morphology. Hence the surface area to volume ratio of the vesicles may specify the presence or absence of cristae-like folds. (c) an increase in the permeability of the membranes to sucrose in the presence of iso-osmotic concentrations of sucrose. (d) an independence of the light transmitted by suspensions of the vesicles from the refractive index of the external medium. This observations run counter to the general previous experience with either mitochondria or liposomes.

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