PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 2160542

Cytoplasmic acidification and activation of Na+/H+ exchange during regulatory volume decrease in Ehrlich ascites tumor cells.

A Livne·E K Hoffmann
View original source ↗Export metadata ↓

Abstract

Ehrlich ascites tumor cells undergoing regulatory volume decrease (RVD) exhibit cytoplasmic acidification as measured by an intracellular fluorescent pH indicator. The acidification results in an activation of the Na+/H+ exchanger. The intracellular pH 'set point' for the activation is estimated to be around 7.0. The activation of the Na+H+ exchanger leads to an incomplete RVD. In support of this conclusion, amiloride and Na+-free medium, known to limit the Na+/H+ exchange, indeed enhance the RVD response. Intracellular acidification and activation of Na+/H+ exchange may be a general response of cells undergoing RVD.

Explore related subjects

AmilorideAnimalsCarcinoma, Ehrlich TumorCarrier ProteinsCytoplasmHydrogen-Ion ConcentrationIon ExchangeMiceOsmolar ConcentrationProtonsSodiumSodium-Hydrogen ExchangersTumor Cells, CulturedJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A Livne, E K Hoffmann. 1990. Cytoplasmic acidification and activation of Na+/H+ exchange during regulatory volume decrease in Ehrlich ascites tumor cells.. https://doi.org/10.1007/bf01869096

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1992

Dopamine D2 receptor stimulation of Na+/H+ exchange assessed by quantification of extracellular acidification.

A microphysiometer was used to quantify the rate of extracellular acidification by C6 glioma cells and L fibroblasts expressing recombinant dopamine D2 receptors. The dopamine D2 receptor agonist, quinpirole, accelerated the rate of acidification of the medium by C6 cells expressing either the short or long form of D2 receptors, D2(415) and D2(444), but not by wild-type cells that were not transfected with a D2 receptor cDNA. The rate of acidification increased with increasing concentrations of quinpirole up to 100 nM. Inhibition of the response by the dopamine D2 antagonist, spiperone, provided additional evidence that the enhanced extracellular acidification resulted from stimulation of D2 receptors. To test the hypothesis that D2 receptor-stimulated extracellular acidification was due to transport of protons by a Na+/H+ antiporter and reflected intracellular alkalinization, the effect of two inhibitors of Na+/H+ exchange, amiloride and methyl-isobutyl-amiloride, was determined. Both compounds inhibited quinpirole-induced extracellular acidification at concentrations that did not alter D2 receptor-mediated inhibition of adenylylcyclase or radioligand binding to D2 receptors. In addition, quinpirole-induced extracellular acidification was greatly inhibited by removal of sodium from the extracellular medium, confirming the participation of Na+/H+ exchange in the extrusion of acid. Quinpirole (100 nM) also increased the rate of extracellular acidification by L cells expressing D2(415), LZR1 cells. Treatment with pertussis toxin (100 ng/ml for 18 h) had no effect on the quinpirole-induced acid extrusion by C6D2(415) and LZR1 cells, although the same pertussis toxin treatment regimen completely prevented inhibition of adenylylcyclase. We conclude that recombinant D2 receptors accelerate Na+/H+ exchange in C6 cells and L fibroblasts by a pathway that does not involve inhibition of adenylylcyclase or pertussis toxin-sensitive G proteins.

Amiloride↗
PubMed1992

Amiloride at pH 7.0 inhibits the Na(+)-driven flagellar motors of Vibrio alginolyticus but allows cell growth.

Amiloride, a specific inhibitor for the Na(+)-driven flagellar motors of alkalophilic Bacillus, is known to inhibit secondarily the growth of alkalophiles. The motility of a marine Vibrio, V. alginolyticus, was almost completely inhibited by 2 mM amiloride either at pH 7.0 or 8.5. We found that this concentration of amiloride inhibited the cell growth completely at pH 8.5 but only slightly at pH 7.0. Kinetic analysis of the inhibition of motility by amiloride at pH 7.0 showed that the inhibition was competitive with Na+ in the medium. Thus, amiloride at pH 7.0 is really a specific and useful tool for the analysis of the Na(+)-driven flagellar motors of Vibrio.

Amiloride↗
PubMed1992

Ca2+ modulates the inhibition of (+)-[3H]isradipine binding by amiloride and quinacrine.

Binding studies were performed to characterize the inhibition by amiloride, 3,4-dichlorobenzamil and quinacrine of specific binding of (+)-[3H]isradipine to L-type voltage-operated calcium ion channels in rat cardiac membranes at 37 degrees C with and without 10(-3) M calcium added. By analysis of saturation, inhibition and dissociation curves we find that without the addition of calcium, amiloride (constant of inhibitor producing 50% inhibition (K0.5) = 6.9 x 10(-4) M, Hill coefficient (nH) = 1.99, k-1 increased) and 3,4-dichlorobenzamil (K0.5 = 7.7 x 10(-7) M, nH = 1.13, k-1 increased) inhibit (+)-[3H]isradipine binding by complex, allosteric interactions, suggesting positive cooperativity between sites for the inhibitors. Quinacrine (K0.5 = 6.7 x 10(-6) M, nH = 0.84, k-1 increased) inhibits the binding allosterically by an action compatible with binding to one site. Addition of 10(-3) M calcium affected the inhibition by amiloride (K0.5 = 1.02 x 10(-3) M, nH = 1.41) and quinacrine (K0.5 = 3.3 x 10(-5) M, nH = 0.65). With calcium added the mechanisms of inhibitions were complex, allosteric, and could be explained by positive cooperativity between sites for amiloride and negative cooperativity between sites for guinacrine. We conclude that calcium addition modulates the inhibitions by amiloride and quinacrine by increasing the inhibition constants and changing the cooperativity.

Amiloride↗