Inhibition of volume-activated chloride currents in endothelial cells by chromones.
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 microM 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 microM. 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 microM 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 cromoglycatemay be due to an intracellular action following its permeation across the cell membrane.
Heinke
S
S
KU Leuven, Laboratorium voor Fysiologie, Belgium.
Szücs
G
G
Norris
A
A
Droogmans
G
G
Nilius
B
B
D000818:Animals; D018927:Anti-Asthmatic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002417:Cattle; D018118:Chloride Channels / Q000037:antagonists & inhibitors*; D004205:Cromolyn Sodium / Q000008:administration & dosage / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009579:Nitrobenzoates / Q000494:pharmacology*; D009994:Osmolar Concentration; D018408:Patch-Clamp Techniques; D011651:Pulmonary Artery / Q000187:drug effects
D018927:Anti-Asthmatic Agents; D018118:Chloride Channels; D009579:Nitrobenzoates; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D004205:Cromolyn Sodium