Inhibition of volume‐activated chloride currents in endothelial cells by chromones

Abstract

1 We have studied the effects of the reported chloride channel blocker, sodium cromoglycate, on volume-activated C1-currents in endothelial cells from bovine pulmonary artery by means of the wholecell patch clamp technique. Cl-currents were activated by challenging the cells with a hypotonic extracellular solution of 60% of the normal osmolarity. 2 Half maximal activation of the current at + 95 mV occurred after exposure of the cells for 148 ± 10 s (n = 6) to hypotonic solution (HTS). At the same membrane potential but in the presence of 100 gM sodium cromoglycate (disodium-1,3-bis (2'-carboxylate-chromone-5'-yloxy)-2-hydroxy-propane) activation was delayed (253 ± 25 s, n = 6) and the maximal current amplitude was reduced to 63 7% of the control (n = 13). 3 In comparison, an equimolar concentration of NPPB (5-nitro-2(3-phenyl) propylamino-benzoic acid), another Cl-channel blocker, completely blocked the volume-activated current in less than 20 s. 4 Sodium cromoglycate, applied at the time when the HTS-induced current was completely activated, dose-dependently inhibited this current with a concentration for half maximal inhibition of 310 70 gM. Data for nedocromil sodium were not significantly different from those for sodium cromoglycate. 5 Sodium cromoglycate, loaded into the endothelial cells via the patch pipette in ruptured patches, resulted in a decline of the HTS activated current with a time course that was compatible with diffusion of the compound from the pipette into the cell. Intracellulary applied sodium cromoglycate was also more effective and at 50 gM caused a decrease in the amplitude of the current to 25 ± 6% (n = 10) of the control current. 6 It is concluded that blockade of volume-activated Cl-currents by extracellular sodium cromoglycate may be due to an intracellular action following its permeation across the cell membrane.

Potent block of volume‐activated chloride currents in endothelial cells by the uncharged form of quinine and quinidine

“…A possible explanation could be that the block is due to an intracellular action following permeation of the uncharged form through the cell membrane, as has been proposed for chromones (Heinke et al, 1995). However, if uncharged quinine or quinidine enters the cell, it would be immediately ionised (the internal solution is at pH 7.2) and the subsequent washout would be rather slow.…”

The Endothelial Volume-Regulated Anion Channel, VRAC

“…There is a huge variety of compounds that inhibit VRAC with moderate affinity (EC 50 between 1 and 1000 µM) and specificity. Among these compounds are not only several classical Cl -channel blockers, such as DIDS, SITS, NPA, 9-AC, NPPB and niflumic acid, but also several "surprising" substances, such as the P-glycoprotein inhibitors tamoxifen, 1,9-dideoxyforskolin, verapamil [17], quinine and quinidine [24], antiallergic drugs from the chromone family [25], the inositol-tetrakisphophates Ins(3,4,5,6)P 4 and Ins(1,4,5,6)P 4 [26], the anti-hypertensive Ca 2+ -antagonist mibefradil [27], and the widely used antidepressant drug fluoxetine, supposed to be a selective serotonin (5-hydroxytryptamine) re-uptake inhibitor [28]. Most of the voltage-independent blockers are relatively hydrophobic aromatic compounds, which can easily permeate the cell membrane.…”

Uroguanylin induces electroencephalographic spikes in rats

“…73, no. 3, p. 623-627 Teixeira, MDA., et al ( Heinke et al, 1995) and these channels are sensitive to nedocromil (Gschwentner et al, 1996). Therefore, we conclude that the neuronal hypersynchronic firing of neurons evoked by uroguanylin is related to a direct effect on chloride channels as discussed above since it is blocked by nedocromil.…”