PERMEATION PROPERTIES AND MODULATION OF VOLUME-ACTIVATED CL- CURRENTS IN HUMAN ENDOTHELIAL-CELLS

1 We have studied the permeation and pharmacological properties of a recently described volume-activated, calcium-insensitive, small-conductance C1(-)-channel in endothelial cells from human umbilical vein. 2 The relative permeability for various anions was I->C1(-)similar to Br->F->gluconate(-) (1.63+/-0.36: 1:0.95+/-0.16:0.46+/-0.04:0.19+/-0.07, n = 10). 3 5-Nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) induced a fast and reversible block of the current (K-I = 29 mu mol l(-1)). 4 Extracellular ATP induced a low-affinity block of the current, that showed a small voltage-dependence (K-I = 4.9 mmol l(-1) at +80 mV and K-I = 8.2 mmol l(-1) at -80 mV) 5 Extracellularly applied arachidonic acid (10 mu mol l(-1)) irreversibly blocked the current in 5 out of 9 cells. This block seems to be non-specific, because other ionic currents, e.g. inwardly rectifying K+ currents, were blocked as well. 6 Tamoxifen induced a high affinity block of the current (K-I = 2.9 mu mol l(-1)). Block and reversal of block were however much slower than with NPPB. 7 Cytotoxic compounds, which are substrates of the P-glycoprotein multidrug transporter, loaded into endothelial cells via the patch pipette, exerted only minor effects on the volume-activated current. Vinblastine and colcemid did not affect the volume-activated current, whereas daunomycin and vincristine induced a slow 'run-down' of the current. 8 The similarity between permeation and pharmacological properties of volume-activated Cl--currents in endothelial cells and those in many other cell types may suggest that they all belong to the same family of volume-activated small-conductance Cl--channels. Evidence that they belong to the class of P-glycoprotein associated Cl--channels is however only marginal, whereas their biophysical characteristics differ significantly from those of the ClC-2 volume-activated Cl--channels.