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H Pasantes-Morales

Publications and source records attributed to H Pasantes-Morales.

At least 73 records · Page 4Linked to original sources
PubMed1992

Role of taurine in neural cell volume regulation.

Release of taurine and other amino acids was monitored from cultured astrocytes and neurons under isosmotic and hyposmotic conditions as well as during exposure of the cells to 56 mM KCl. The release was correlated with swelling, as determined by the 3-O-methylglucose method. It was shown that release of taurine from astrocytes cultured from cerebral cortex and cerebellum of rats and mice regardless of the stimulating agent is a consequence of cell swelling. The release is unrelated to depolarization. This conclusion is also valid regarding release of taurine from cerebellar granule neurons. Comparison of release of different amino acids showed that not only taurine but also to some extent glutamate, aspartate, and glycine are released during cell swelling. On the other hand, glutamine is not released under these conditions. Studies of uptake of taurine under isosmotic and hyposmotic conditions as well as the dependency of the release on sodium and temperature strongly suggest that the release process is mediated by diffusional forces and not by a reversal of the high-affinity carrier. It is proposed that taurine may play an important role as an osmotically active substance in the brain involved in cell volume regulation.

Amino Acids↗
PubMed1991

Hyposmolarity-activated fluxes of taurine in astrocytes are mediated by diffusion.

In order to obtain information about the mechanism responsible for swelling associated taurine release in astrocytes, the kinetics of taurine uptake in cultured astrocytes from mouse cerebral cortex was studied under isosmotic and hyposmotic (50% osmolarity) conditions. It was found that the Vmax for the high affinity component of taurine uptake was unaffected by exposure of the astrocytes to hyposmotic conditions and that the Km value was somewhat increased. Contrary to Vmax, the non-saturable component of the uptake was greatly increased (2.5-fold) after exposure of the cells to hyposmotic media leading to cell swelling. In addition to the kinetic characterization of taurine uptake the actual intracellular taurine content after incubation (15 min) in isosmotic or hyposmotic media with different taurine concentrations (0-100 mM) under Na(+)-free conditions was determined. At taurine concentrations less than 30 mM corresponding to the intracellular content in cells not exposed to taurine, exposure to hyposmotic media led to a decrease in the intracellular taurine content. At higher external taurine concentrations (greater than 30 mM) the intracellular taurine contents were dramatically increased after exposure to hyposmotic conditions. The increase in intracellular taurine seen under hyposmotic conditions at 100 mM external taurine could be significantly reduced by 100 microM DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonate). Altogether these results suggest that a diffusional process rather than the high affinity taurine carrier is involved in the swelling induced increase in astrocytic taurine influx and efflux.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Taurine release associated to volume regulation in rabbit lymphocytes.

Rabbit lymphocytes exposed to hyposmotic media first swell and then recover their initial volume within 6 min. During volume recovery, free amino acids (FAA) decrease from 451.1 to 208 nmoles/mg protein. Taurine was the dominating FAA, accounting for 70% of the FAA pool. The time course of 3H-taurine release induced by hyposmolarity followed that of volume recovery. Efflux of 3H-taurine in an 8 min period was 17.8% (of total labeled taurine accumulated during loading) in an isosmotic medium. Reducing osmolarity to 0.87, 0.75, 0.62, and 0.5 increased this release to 24.8%, 38.1%, 56.4% and 70.9%, respectively. The volume-sensitive release of 3H-taurine was unaffected by omission of external Na+ or Ca++ and was reduced by 23% in the absence of Cl-. It was unaffected by agents disrupting the cytoskeleton or by tetraethylammonium, barium, quinidine, and gadolinium, but was 26% reduced by DIDS. Taurine release was inhibited at 4 degrees C, but was unchanged at 15 degrees C or 25 degrees C. An involvement of FAA, particularly taurine, in lymphocyte volume regulation is suggested.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Taurine-deficient cultured cerebellar astrocytes and granule neurons obtained by treatment with guanidinoethane sulfonate.

Mouse cerebellar granule neurons and astrocytes grown in the presence of 2 mM guanidinoethane sulfonate (GES) exhibited a progressive and rapid decrease in taurine concentration. A reduction of 20% was observed as early as 1 hr after exposure to GES and the loss of cell taurine continued until the taurine pool was reduced by about 90%. This remaining taurine persisted without further decrease even after 3 weeks of exposure to GES. Taurine reduction caused by GES was similar in both types of cells. The effect of GES was dose-dependent, with significant decreases in taurine levels already detected at 100 microM. It was selective for taurine, since none of the other free amino acids were affected. Taurine depletion induced by GES was totally reversible. Intracellular taurine was not mobilized by GES. Taurine uptake in both astrocytes and granule neurons, examined at the taurine concentration present in the culture medium, was practically abolished by 2 mM GES. This approach represents an in vitro model of taurine depletion that may be useful to investigate the cell abnormalities responsible for the failure of differentiation and migration of granule cells and astrocytes observed in taurine-deficient cats.

Amino Acids↗
PubMed1991

Hyposmolarity-induced taurine release in cerebellar granule cells is associated with diffusion and not with high-affinity transport.

The effects of hyposmotic conditions on taurine uptake and release were studied in mice cultured cerebellar granule cells. The effect of DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonate) and of the divalent cations Mg++ and Mn++ on the hyposmolarity-induced changes in these parameters was investigated. Mg++ (20 mM) and Mn++ (5 mM) inhibited by 25% and 41%, respectively, the release of taurine observed in 30% hyposmolar media. DIDS (100 microM) inhibited this release by 46%. Taurine efflux evoked by 50% hyposmolar solutions was reduced about 40% by Mg++ and 55% by Mn++. Taurine uptake into the granule cells could be resolved into a high-affinity carrier-mediated component plus a nonsaturable diffusion component. The kinetic constants (Km and Vmax) for the high-affinity uptake were unaffected by a 50% decrease in the osmolarity. The diffusion constant for the nonsaturable taurine uptake was increased from 1.5 x 10(-4) in isosmotic media to 4.6 x 10(-4) ml x min-1 x mg-1 in hyposmotic (50%) media. This increase in the diffusional component of taurine uptake elicited by the hyposmotic condition was inhibited approximately 25% by either 100 microM DIDS or 5 mM Mn++. These results strongly suggest that the increase in taurine release induced by swelling under hyposmotic conditions is mediated by a diffusional process and not by a reversal of the high-affinity taurine carrier.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Osmolarity-sensitive release of free amino acids from cultured kidney cells (MDCK).

The amino acid pool of MDCK cells was essentially constituted by alanine, glycine, glutamic acid, serine, taurine, lysine, beta-alanine and glutamine. Upon reductions in osmolarity, free amino acids were rapidly mobilized. In 50% hyposmotic solutions, the intracellular content of free amino acids decreased from 69 to 25 mM. Glutamic acid, taurine and beta-alanine were the most sensitive to hyposmolarity, followed by glycine, alanine and serine, whereas isoleucine, phenylalanine and valine were only weakly reactive. The properties of this osmolarity-sensitive release of amino acids were examined using 3H-taurine. Decreasing osmolarity to 85, 75 or 50% increased taurine efflux from 0.6% per min to 1.6, 3.5 and 5.06 per min, respectively. The time course of 3H-taurine release closely follows that of the regulatory volume decrease in MDCK cells. Taurine release was unaffected by removal of Na+, Cl- or Ca2+, or by treating cells with colchicine or cytochalasin. It was temperature dependent and decreased at low pH. Taurine release was unaffected by bumetanide (an inhibitor of the Na+/K+/2Cl- carrier); it was inhibited 16 and 67 by TEA and quinidine (inhibitors of K+ conductances), unaffected by gadolinium or diphenylamine-2-carboxylate (inhibitors of Cl- channels) and inhibited 50% by DIDS. The inhibitory effects of DIDS and quinidine were additive. Quinidine but not DIDS inhibited taurine uptake by MDCK cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Similar properties of taurine release induced by potassium and hyposmolarity in the rat retina.

Increasing external K+ concentration to 56, 75 or 100 mM stimulated taurine release by 3-, 7- and 11-fold, respectively. The K(+)-evoked release of [3H]taurine was markedly delayed, sustained and Ca(2+)-independent, in clear contrast to the usual neurotransmitter release pattern. These high K+ concentrations caused a marked increase in retinal cell volume which was prevented by removal of Cl-, or in hyperosmotic solutions. In these conditions [3H]taurine release also was abolished, suggesting an association of taurine efflux and cell swelling. Taurine release was also markedly increased 10- and 20-fold upon reduction of external osmolarity by 25 and 50%, respectively. Both, K(+)- and hyposmolarity-induced release were markedly inhibited by DIDS and quinidine. Total inhibition of the K(+)-evoked release was observed at 200 microM DIDS or 1 mM quinidine, whereas the drugs inhibited the hyposmolarity-evoked release by 50 and 68% respectively, at these concentrations. It is suggested that swelling is the signal for the K(+)-induced taurine release from rat retina.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Volume-sensitive release of taurine from cultured astrocytes: properties and mechanism.

Release of taurine in response to cell swelling induced by hyposmolarity was observed in cultured astrocytes. Efflux of 3H-taurine increased by 30% and 70% upon reductions in osmolarity of only 5% and 10%. Reductions in osmolarity of 20%, 30%, and 50% stimulated basal taurine release by 300%, 500%, and 1,500%, respectively. The properties of this volume-sensitive release of taurine were examined to investigate: 1) its association with K+ and Cl- fluxes, currently activated during volume regulation: 2) its relationship with Ca2(+)-dependent reactions; and 3) the mechanism of the taurine efflux process. Taurine release was unaffected by removal of Na+, Ca2+, or Cl-, by pimozide and trifluoperazine, or by agents disrupting the cytoskeleton. The K+ channel inhibitors barium, quinidine, tetraethylammonium, and gadolinium had no effect. Taurine release was reduced by furosemide, a blocker of K+/Cl- cotransport, but not by the more specific inhibitor, bumetanide. It was markedly reduced by the inhibitors of Cl- channels DIDS, SITS, and anthracene-9-carboxylate. Taurine efflux was pH-dependent, being reduced at low pH values. It was decreased at 4 degrees C but not at 14 degrees C or 20 degrees C. These results suggest that the volume-sensitive release of taurine is independent of K+ fluxes but may be associated with Cl- conductances. It also seems unrelated to Ca2(+)-dependent transduction mechanisms. The Na(+)-dependent taurine carrier apparently is not involved in the swelling-induced release process.

Animals↗
PubMed1990

Potassium-stimulated release of taurine from cultured cerebellar granule neurons is associated with cell swelling.

Effects of increased concentrations of potassium and of hyposmolar conditions on release of taurine were investigated in cerebellar granule neurons cultured from mice. It was found that increases in the external potassium concentration as well as decreases in osmolarity dose-dependently increased release of exogenously supplied [3H]-taurine and endogenous taurine from the neurons. The release of endogenous taurine elicited by a reduction of the osmolarity of the incubation media to 70% or 50% was much more pronounced than that of other amino acids, particularly glutamine, the release of which was not affected at all. The potassium-stimulated release of [3H]-taurine was strictly chloride dependent and it was inhibited by an increase of the osmolarity of the media as well as by 4,4'-diisothyocyanostilbene-2,2'-disulfonate (DIDS) (100 microM). Moreover, a similar increase in the potassium concentration led to an increase in intracellular volume (swelling), a process which was also chloride dependent. It is concluded that potassium-stimulated taurine release from cerebellar granule neurons is associated with cell volume changes and that taurine is likely to play a role as an osmotically active substance in these neurons.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Chloride dependence of the K(+)-stimulated release of taurine from synaptosomes.

Exposure of a crude synaptosomal fraction to K+ concentrations ranging from 25 to 100 mM evokes the release of [3H]taurine and [3H]GABA. These high concentrations of K+ induce, besides depolarization, a marked synaptosomal swelling, which is prevented by replacing chloride in the solutions with the largely impermeant anion gluconate. The depolarizing effect of K+ is unaffected by omission of chloride. The K(+)-evoked release of taurine seems related to K(+)-induced changes in synaptosomal volume rather than to a depolarizing effect, since it is totally calcium-independent but is abolished by reducing chloride and by making solutions hypertonic with mannitol. The release of [3H]GABA, in contrast is unaffected in chloride-free or hypertonic solutions.

Animals↗
PubMed1989

Release of taurine from astrocytes during potassium-evoked swelling.

Cultured astrocytes superfused with isosmotic solutions containing high concentrations of potassium, i.e., 25, 56, 75, and 100 mM, showed a proportional increase in cell volume corresponding to 25, 36, 57, and 75% greater than the cell volume in physiological solutions. This volume increase was abolished in low chloride or hypertonic solutions. The release of 3H-taurine previously accumulated by astrocytes was stimulated by potassium at all concentrations examined. During 4-minute exposure to 25, 56, 75, or 100 mM of potassium, cells released 13.5, 15.6, 20.2, or 36.2%, respectively, of the total labeled taurine accumulated during the preloading period. The potassium-stimulated release of 3H-taurine was calcium-independent and insensitive to BaCl2 and bumetanide. Substitution of chloride by gluconate to concentrations necessary to maintain the K+ X Cl- product constant abolished the potassium-stimulated release of 3H-taurine. Superfusion with solutions made hypertonic with sucrose also decreased the potassium-elicited efflux of 3H-taurine. In both conditions, the depolarizing effect of potassium measured with 3H-TPP+ was unchanged. High potassium concentrations and hyposmotic solutions released 3H-taurine by a nonadditive mechanism. These results indicate that in cultured astrocytes high concentrations of potassium produce both swelling and depolarization, but only swelling elicits the release of taurine. These observations suggest an involvement of taurine in cell-volume regulation in astrocytes.

Animals↗
PubMed1989

A volume-dependent, chloride-sensitive component of taurine release stimulated by potassium from retina.

Chick retinas exposed to 56 mM KCl showed marked swelling of cells and synaptic structures, detected by morphological examination as well as by measurements of cell water content. Retinal cell swelling is prevented by omission of chloride. Potassium chloride, 56 mM, elicited the efflux of [3H]taurine by a process that is partly calcium-dependent, highly chloride-dependent (80%), and sensitive to furosemide. The release of [3H]dopamine under the same conditions is completely calcium-dependent and increases in the absence of chloride. The chloride-dependent component of [3H]taurine efflux seems related to increases in volume changes since it is markedly reduced when cell swelling is prevented either by maintaining constant the K X Cl product (Donnan equilibrium) or by making the solution hypertonic with mannitol. Omission of calcium and of chloride showed additive effects, practically suppressing the potassium-stimulated release of taurine. These results suggest that the potassium-stimulated efflux of [3H]taurine consists of a large component associated to changes in cell volume and a small component probably related to the depolarizing effects of potassium.

Animals↗