ABSTRACT
Primary cultures of rat cortical astrocytes undergo a swelling-activated loss of taurine and creatine. In this study, the pharmacological characteristics of the taurine and creatine efflux pathways were compared, and significant differences were shown to exist between the two. Both taurine and creatine effluxes were rapidly activated upon exposure of astrocytes to hypo-osmotic media, and rapidly inactivated upon their return to iso-osmotic media. The relative rates of taurine and creatine efflux depended upon the magnitude of the hypo-osmotic shock. Anion-transport inhibitors strongly inhibited taurine efflux, with the order of potency being NPPB > DIDS > niflumic acid. DIDS and NPPB had less of an inhibitory effect on creatine efflux, whereas tamoxifen and niflumic acid actually stimulated creatine efflux. These data are consistent with separate pathways for taurine and creatine loss during astrocyte swelling.
Subject(s)
Astrocytes/metabolism , Creatine/metabolism , Organic Anion Transporters/metabolism , Taurine/metabolism , 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid/pharmacology , Animals , Animals, Newborn , Anions/metabolism , Astrocytes/cytology , Astrocytes/drug effects , Biological Transport , Cells, Cultured , Cerebral Cortex/cytology , Nitrobenzoates/pharmacology , Organic Anion Transporters/antagonists & inhibitors , Osmotic Pressure , Rats , Time FactorsABSTRACT
How do plant cells accomplish a net uptake of Ca(2+) but keep the membrane potential under control? Consideration of the voltage dependence of the depolarization-activated calcium channel and hyperpolarization-activated calcium channel types, and two other major transporters in the plasma membrane, the H(+)-ATPase and I(K,out), suggests that one channel is well suited for both nutritive and signalling Ca(2+) uptake whereas the other could be limited to a signalling function.
Subject(s)
Calcium Channels/metabolism , Calcium/metabolism , Ion Pumps/physiology , Potassium Channels, Tandem Pore Domain , Arabidopsis/metabolism , Arabidopsis Proteins , Patch-Clamp Techniques , Plant Proteins/metabolism , Potassium Channels/metabolism , Proton-Translocating ATPases/genetics , Proton-Translocating ATPases/metabolismABSTRACT
The chloride channel antagonists anthracene-9-carboxylic acid, ethacrynic acid and niflumic acid were found to be fungistatic and morphogenic when tested against the ascomycete Neurospora crassa. Potency increased with decreasing pH, suggesting that the protonated forms of the compounds were active. Niflumic acid produced the most pronounced growth aberrations which may reflect an ability to acidify the cytoplasm and block the plasma membrane anion channel of N. crassa.
Subject(s)
Anthracenes/pharmacology , Chloride Channels/antagonists & inhibitors , Ethacrynic Acid/pharmacology , Neurospora crassa/cytology , Neurospora crassa/drug effects , Niflumic Acid/pharmacology , Agar , Antifungal Agents/pharmacology , Biomass , Cell Division/drug effects , Culture Media , Hydrogen-Ion Concentration , Neurospora crassa/growth & development , Neurospora crassa/metabolismABSTRACT
A decrease in the intracellular levels of osmotically active species has invariably been seen after swelling of mammalian brain tissue preparations. The exact identity of the species, and the manner of their decrease, remain to be described. We investigated the swelling-activated decrease of organic osmolytes in rat cortical brain slices using (1)H- and (31)P-magnetic resonance spectroscopy. We found that acute hypo-osmotic shock causes decreases in the levels of a range of intracellular amino acids and amino acid derivatives, N-acetyl-aspartate, creatine, GABA, glutamate, hypotaurine, and also in the levels of the methylamines glycerol-phosphorylcholine, phosphorylcholine and choline. Incubation of cortical slices with the anion channel blockers niflumic acid and tamoxifen caused inhibition of organic osmolyte efflux, suggesting that such osmolyte efflux occurs through anion channels. Intracellular phosphocreatine was also seen to decrease during acute hypo-osmotic superfusion, although intracellular ATP remained constant. In addition, the acidification of an intracellular compartment was observed during hypo-osmotic superfusion. Our results suggest a link between brain energy reserve and brain osmoregulation.
