Swelling and potassium uptake in cultured astrocytes

1987 ◽  
Vol 65 (5) ◽  
pp. 1051-1057 ◽  
Author(s):  
Wolfgang Walz
Keyword(s):  
Energy Source ◽  
Driving Force ◽  
Primary Cultures ◽  
Volume Changes ◽  
Cultured Astrocytes ◽  
High K ◽  
Ion Activity ◽  
Net Uptake ◽  
Two Phases ◽  
External K

The intracellular water content of astrocytes in primary cultures shows a biphasic swelling pattern on exposure to various increased external K+ concentrations over the range of 1.5–100 mM. The two phases (physiological, 1.5–12 mM K+; pathological, 25–100 mM K+) are based on two different mechanisms. Both can be blocked by low Cl− solutions and involve intensive net uptake of K+. However, the physiological phase consists of the activation of a KCl + NaCl carrier, while the Na+ in turn is pumped out by Na+–K+ ATPase, with a resultant net accumulation of KCl. At pathological K+ concentrations the KCl + NaCl carrier is less active because the Na+ driving force, its energy source, is reduced (owing to depolarization by K+). However, the Donnan equilibrium across the cell membrane is heavily disturbed, which leads to passive KCl accumulation. The results suggest that volume changes in cultured glial cells during exposure to high K+ should be taken into consideration since they disguise K+ accumulation when only ion activity is measured.

Role of Na/K/Cl cotransport in astrocytes

1992 ◽  
Vol 70 (S1) ◽  
pp. S260-S262 ◽  
Author(s):  
Wolfgang Walz
Keyword(s):  
Volume Regulation ◽  
Ion Homeostasis ◽  
Combined Cycle ◽  
Kinetic Characterization ◽  
Cultured Astrocytes ◽  
Net Uptake ◽  
Swelling Volume ◽  
External K

The kinetic characterization of the Na/K/Cl cotransport of cultured astrocytes and evidence for its involvement in volume regulation and K+ net uptake during K+ clearance are reviewed. Emphasis is put on experimental evidence for a proposed sodium cycle in astrocytes; this cycle involves a Na+–K+ ATPase that is stimulated by both a high external K+ and intracellular Na+. Elevated external K+ also stimulates the Na/K/Cl carrier, transporting these ions inward. As a result Na+ is cycled across the membrane, carried inward by the Na/K/Cl carrier, and returned by the Na+–K+ ATPase. Both functionally coupled mechanisms lead to intracellular KCl accumulation and inward movements of water to compensate for increased osmolarity. The combined cycle is expected to play a major role in the regulation of physiological K+ levels in the brain.Key words: furosemide, ion homeostasis, Na+–K+ ATPase, swelling, volume regulation.

scholarly journals Intense Furosemide-Sensitive Potassium Accumulation in Astrocytes in the Presence of Pathologically High Extracellular Potassium Levels

1984 ◽  
Vol 4 (2) ◽  
pp. 301-304 ◽  
Author(s):  
Wolfgang Walz ◽  
Leif Hertz
Keyword(s):  
Primary Cultures ◽  
Volume Control ◽  
Extracellular Potassium ◽  
Potassium Accumulation ◽  
Kcl Cotransport ◽  
Extracellular Compartment ◽  
Cultured Astrocytes ◽  
External K

An intense K+ accumulation in primary cultures of astrocytes, occurring when external K+ was increased from 5.4 to 54 m M, was investigated. This increase resulted in a doubling of the K+ content within 10 s. Thirty percent of the accumulation was inhibited by furosemide (2 m M). This drug had no effect on the unidirectional influx of K+ at 5.4 m M K+, but when the extracellular K+ concentration was increased, there appeared to be a furosemide-sensitive component of the influx. This component increased with increasing external K+ levels, reaching 44% of the total influx at 72 m M. These results show that astrocytes exhibit an intense furosemide-sensitive K+ accumulation which is activated by K+ levels resembling those occurring in the extracellular compartment during pathological events. Previous studies on a furosemide-sensitive Cl− pump in cultured astrocytes suggest that this accumulation might be via KCl cotransport, which in other systems is involved in volume control.

scholarly journals L-type voltage-dependent Ca2+ channels in cerebral microvascular endothelial cells and ET-1 biosynthesis

2002 ◽  
Vol 283 (6) ◽  
pp. C1687-C1695 ◽  
Author(s):  
Momoh A. Yakubu ◽  
Charles W. Leffler
Keyword(s):  
Endothelial Cells ◽  
Primary Cultures ◽  
Chelating Agent ◽  
Microvascular Endothelial Cells ◽  
Vasoactive Agents ◽  
Cerebral Microvessels ◽  
Thromboxane Receptor ◽  
High K ◽  
Voltage Dependent ◽  
Microvascular Endothelial

We investigated the role of intracellular calcium concentration ([Ca2+]i) in endothelin-1 (ET-1) production, the effects of potential vasospastic agents on [Ca2+]i, and the presence of L-type voltage-dependent Ca2+ channels in cerebral microvascular endothelial cells. Primary cultures of endothelial cells isolated from piglet cerebral microvessels were used. Confluent cells were exposed to either the thromboxane receptor agonist U-46619 (1 μM), 5-hydroxytryptamine (5-HT; 0.1 mM), or lysophosphatidic acid (LPA; 1 μM) alone or after pretreatment with the Ca2+-chelating agent EDTA (100 mM), the L-type Ca2+ channel blocker verapamil (10 μM), or the antagonist of receptor-operated Ca2+ channel SKF-96365 HCl (10 μM) for 15 min. ET-1 production increased from 1.2 (control) to 8.2 (U-46619), 4.9 (5-HT), or 3.9 (LPA) fmol/μg protein, respectively. Such elevated ET-1 biosynthesis was attenuated by verapamil, EDTA, or SKF-96365 HCl. To investigate the presence of L-type voltage-dependent Ca2+channels in endothelial cells, the [Ca2+]isignal was determined fluorometrically by using fura 2-AM. Superfusion of confluent endothelial cells with U-46619, 5-HT, or LPA significantly increased [Ca2+]i. Pretreatment of endothelial cells with high K+ (60 mM) or nifedipine (4 μM) diminished increases in [Ca2+]i induced by the vasoactive agents. These results indicate that 1) elevated [Ca2+]i signals are involved in ET-1 biosynthesis induced by specific spasmogenic agents, 2) the increases in [Ca2+]i induced by the vasoactive agents tested involve receptor as well as L-type voltage-dependent Ca2+ channels, and 3) primary cultures of cerebral microvascular endothelial cells express L-type voltage-dependent Ca2+ channels.

Calcium transport across peritubular surface of the marine teleost renal tubule

1978 ◽  
Vol 234 (6) ◽  
pp. F522-F531 ◽  
Author(s):  
J. L. Renfro
Keyword(s):  
Divalent Cation ◽  
Cytochalasin B ◽  
Slow Phase ◽  
Renal Tubules ◽  
Free Medium ◽  
Pseudopleuronectes Americanus ◽  
High K ◽  
Ca Uptake ◽  
Two Phases ◽  
Secretory System

Isolated renal tubules of seawater-acclimated flounder (Pseudopleuronectes americanus) readily accumulated Ca and Mg when exposed to increased concentrations of these ions. Evidence based on the ability of the tubules to maintain high K levels indicated that the Ca was neither free in the cytosol nor taken up by mitochondria. Two phases of Ca uptake were seen. The fast phase was kinetically complex and not affected by Mg, dinitrophenol, cytochalasin B, or Na-free medium, but was stimulated by ouabain. The slow phase showed Michaelis-Menten kinetics and was inhibited by Mg and dinitrophenol, but was stimulated by Na-free medium, cytochalasin B, and ouabain. The slow phase was also more responsive to changes in bath Ca activity and was thought to be involved with the powerful divalent cation secretory system of these tubules. No correlation between divalent cation uptake and fluid content of the tubules was seen.

scholarly journals Glycogen serves as an energy source that maintains astrocyte cell proliferation in the neonatal telencephalon

2016 ◽  
Vol 37 (6) ◽  
pp. 2294-2307 ◽  
Author(s):  
Hitoshi Gotoh ◽  
Tadashi Nomura ◽  
Katsuhiko Ono
Keyword(s):  
Energy Source ◽  
Cell Proliferation ◽  
Glycogen Phosphorylase ◽  
Cell Cycle Progression ◽  
Neuronal Development ◽  
Kinase Inhibitors ◽  
Primary Cultures ◽  
Glycogen Metabolism ◽  
Radial Glial Cells

Large amounts of energy are required when cells undergo cell proliferation and differentiation for mammalian neuronal development. Early neonatal mice face transient starvation and use stored energy for survival or to support development. Glycogen is a branched polysaccharide that is formed by glucose, and serves as an astrocytic energy store for rapid energy requirements. Although it is present in radial glial cells and astrocytes, the role of glycogen during development remains unclear. In the present study, we demonstrated that glycogen accumulated in glutamate aspartate transporter (GLAST)+ astrocytes in the subventricular zone and rostral migratory stream. Glycogen levels markedly decreased after birth due to the increase of glycogen phosphorylase, an essential enzyme for glycogen metabolism. In primary cultures and in vivo, the inhibition of glycogen phosphorylase decreased the proliferation of astrocytic cells. The number of cells in the G1 phase increased in combination with the up-regulation of cyclin-dependent kinase inhibitors or down-regulation of the phosphorylation of retinoblastoma protein (pRB), a determinant for cell cycle progression. These results suggest that glycogen accumulates in astrocytes located in specific areas during the prenatal stage and is used as an energy source to maintain normal development in the early postnatal stage.

pH regulatory transport systems in a smooth muscle-like cell line

1990 ◽  
Vol 258 (3) ◽  
pp. C470-C479 ◽  
Author(s):  
R. W. Putnam
Keyword(s):  
Prolonged Exposure ◽  
Ph Regulation ◽  
Transport Systems ◽  
Disulfonic Acid ◽  
High K ◽  
Recovery From Acidification ◽  
Ethanesulfonic Acid ◽  
Membrane Transport Systems ◽  
External Ph ◽  
External K

The membrane transport systems responsible for pH regulation in BC3H-1 cells were studied using the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF). In nominally CO2-free Na N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid buffer (NHB) recovery from acidification after an NH4Cl pulse was reversibly inhibited by 1 mM amiloride or by Na-free solutions. On exposure to 5% CO2-HCO3 (external pH constant at 7.4), BC3H-1 cells alkalinized by approximately 0.3-0.4 pH unit. This CO2-induced alkalinization was unaffected by 1 mM amiloride, markedly reduced by 0.5 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), and inhibited by Na-free solutions. On readdition of Na, cells rapidly alkalinized, even in the presence of 1 mM amiloride. Exposure to Cl-free CO2-HCO3 solutions caused a rapid alkalinization of nearly 1 pH unit that was abolished by SITS, largely independent of Na, unaffected by amiloride, and unchanged by membrane depolarization in high external K solutions. CO2-induced alkalinization was slowed by approximately 75% after prolonged exposure of cells to Cl-free NHB, but a distinct recovery from acidification remained in these Cl-depleted cells. This recovery was Na-dependent, SITS-inhibitable, and unaffected by depolarization in high-K solutions. In the presence of CO2, the acidification seen in response to NH4Cl-induced alkalinization was reduced 50% by 0.5 mM SITS. These data suggest that the regulation of pH in BC3H-1 cells is mediated by at least three transport systems: 1) Na-H exchange; 2) Cl-HCO3 exchange; and 3) electroneutral (Na + HCO3)-Cl exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute reductions in PO2 depolarize pulmonary artery endothelial cells and decrease [Ca2+]i

1994 ◽  
Vol 266 (4) ◽  
pp. H1416-H1421 ◽  
Author(s):  
T. Stevens ◽  
D. N. Cornfield ◽  
I. F. McMurtry ◽  
D. M. Rodman
Keyword(s):  
Endothelial Cells ◽  
Membrane Potential ◽  
Pulmonary Artery ◽  
Driving Force ◽  
Primary Cultures ◽  
K Channel ◽  
Channel Blockers ◽  
Electrochemical Gradient ◽  
Similar Reduction ◽  
Fura 2

Whereas pulmonary artery endothelial cells (PAECs) are sensitive to oxygen, neither the effect of an acute reduction in PO2 on PAEC membrane potential nor its effect on intracellular free Ca2+ ([Ca2+]i) is known. We hypothesized that in confluent primary cultures of PAECs, an acute decrease in PO2 would depolarize the cell membrane, inhibit Ca2+ influx, and reduce [Ca2+]i. To test this hypothesis, the membrane-sensitive fluorophore bis (1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4, 1 microM) and [Ca2+]i-sensitive probe fura 2 (3 microM) were used. A decrease in PO2 from 125 to 35 mmHg caused membrane depolarization and a 60 +/- 8% (data are means +/- SE) reduction in Ca2+ influx, estimated by manganese quenching of fura 2 fluorescence. While basal [Ca2+]i was 79 +/- 5 nM in normoxic cells, it decreased to 31 +/- 2 nM after 15 min of hypoxia. Decreasing the electrochemical gradient for Ca2+ entry with either low extracellular Ca2+, the K+ channel blockers tetraethylammonium or charybdotoxin, or blockade of Ca2+ entry with lanthanum decreased [Ca2+]i by 54-71% of that observed during an acute reduction in PO2. These results demonstrate that an acute reduction in PO2 1) depolarizes PAECs, 2) reduces Ca2+ influx, and 3) decreases [Ca2+]i, and that a similar reduction in [Ca2+]i was observed with interventions designed to reduce the electrochemical driving force for Ca2+ entry.

Epinephrine modifications of insulin release and of 86Rb+ or 45Ca2+ fluxes in rat islets

1983 ◽  
Vol 244 (3) ◽  
pp. E245-E252 ◽  
Author(s):  
T. Tamagawa ◽  
J. C. Henquin
Keyword(s):  
Amino Acid ◽  
Insulin Release ◽  
Maximum Effect ◽  
Rat Islets ◽  
High K ◽  
Net Uptake ◽  
Insulinotropic Effect ◽  
Camp Levels ◽  
K Permeability ◽  
86Rb Influx

The effects of epinephrine on insulin release, 86Rb+ fluxes, and 45Ca2+ fluxes were measured in rat islets. In the presence of 10 mM glucose, epinephrine did not affect 86Rb+ influx and slightly increased net uptake. It caused a monophasic inhibition of release and a biphasic decrease in 86Rb+ efflux. A maximum effect was observed with 1 microM epinephrine, but release was more markedly inhibited by lower concentrations of the catecholamine than was the efflux. Epinephrine inhibition of release and efflux was reversed by phentolamine and yohimbine but not by prazosin or propranolol. It was mimicked by norepinephrine and clonidine. The inhibition of 86Rb+ efflux persisted when insulin release was prevented by omission of extracellular calcium. Ouabain or high K+ markedly increased 86Rb+ efflux in the presence of glucose and epinephrine; theophylline and quinine had a similar but smaller effect. None of these agents restored insulin release. Epinephrine abolished the insulinotropic effect of arginine without altering the rise in 86Rb+ efflux triggered by the amino acid. Epinephrine abolished insulin release but inhibited 45Ca2+ efflux only partially during stimulation by glucose or by barium plus theophylline. The results show that epinephrine does not inhibit insulin release by activating the Na pump or by increasing K permeability of the B cell membrane. On the contrary, the inhibition of release is accompanied by a decrease in 86Rb+ efflux. Both result from activation of alpha 2-receptors but are not causally related; they could be due to remodeling of Ca2+ fluxes and/or changes in cAMP levels.

Interstitial volume changes during spreading depression (SD) and SD-like hypoxic depolarization in hippocampal tissue slices

1994 ◽  
Vol 71 (6) ◽  
pp. 2548-2551 ◽  
Author(s):  
J. Jing ◽  
P. G. Aitken ◽  
G. G. Somjen
Keyword(s):  
Spreading Depression ◽  
Volume Changes ◽  
Tissue Slices ◽  
Ion Concentrations ◽  
Ca1 Region ◽  
Interstitial Volume ◽  
High K ◽  
Concentration Changes ◽  
Short Time ◽  
Total Tissue

1. Relative interstitial volume (ISV) was estimated from the concentration changes of iontophoretically administered tetramethyl- and tetraethylammonium (TMA+ and TEA+). Spreading depression (SD) was provoked by high K+, and hypoxic SD-like depolarization (HSD) was induced by withdrawing oxygen. 2. Probe ion concentrations increased dramatically and about equally during SD and HSD, except that in a few hypoxic trials signals became transiently smaller than control. Interstitial volume appeared to decrease on the average by approximately 70%. 3. The ISV that remains patent in CA1 region at the height of SD is < 4% of total tissue volume. Probe ions may occasionally have passed through cell membranes for a short time during hypoxic SD.

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