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

摘要

1. We have studied the effects of the reported chloride channel blocker, sodium cromoglycate, on volume-activated Cl~- currents in endothelial cells from bovine pulmonary artery by means of the whole-cell 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 μm 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 μM. 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 μM 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.