Permeation properties and modulation of volume‐activated Cl⁻‐currents in human endothelial cells

Abstract

1 We have studied the permeation and pharmacological properties of a recently described volumeactivated, calcium-insensitive, small-conductance Cl--channel 4 Extracellular ATP induced a low-affinity block of the current, that showed a small voltagedependence (K, = 4.9 mmol 1-at + 80 mV and K, = 8.2 mmol 1`at -80 mV). 5 Extracellularly applied arachidonic acid (10 imol 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, = 2.9 pmol 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 CIC-2 volume-activated Cl--channels.

Multiple Types of Chloride Channels in Bovine Pulmonary Artery Endothelial Cells

“…Swelling of CPAE cells activates large currents, which have been identified as Cl* currents and described in detail elsewhere [5][6][7]. Figure 1 shows an example of a cell challenged with a 28% hypotonic 'mannitol Krebs' solu tion, in which we measured simultaneously the changes in Cl* Channels in Endothelial Cells these experiments -36 mV).…”

“…Volume-activated Cl* currents, Ici, VOi> have already been described in detail in endothelial cells [1,[5][6][7][8]. Their activation requires a permissive concentration of intracellular Ca2+, [Ca2+]i: below this threshold, Iq .voi is not activated by changes in cell volume, above it, how ever, the current is not modulated by Ca2+ [9], These cur rents are obviously not only activated by swelling but also by Ca2+-dependent changes in cell shape in response to mechanical or humoral stimulation [6,10], which ren ders the dissection of possibly Ca2+-activated Cl* chan nels difficult.…”

Ca²⁺ Nanodomain-Mediated Component of Swelling-Induced Volume-Sensitive Outwardly Rectifying Anion Current Triggered by Autocrine Action of ATP in Mouse Astrocytes

“…At this concentration, almost all of the ATP-sensitive purinergic receptors would be activated [28,32]. Furthermore, it is known that high concentrations of extracellular ATP at >1 mM levels may directly block VSOR channels in a voltage-dependent manner [33][34][35] was removed) were included in the DCPIB treatment (filled symbols) under the conditions shown in A (squares) and B (triangles). The amplitudes of the currents before the DCPIB treatment in both conditions were so large that the remaining components after the DCPIB treatment (11.9 ± 2.7 pA pF -1 at +100 mV in A, n = 15, and 14.5 ± 2.8 pA pF -1 in B, n = 13) were negligibly small.…”

Intracellular Signalling Involved in Volume Regulatory Decrease

“…Depolarisation-induced inactivation is extensive in rat C6 glioma cells [20], essentially absent in Jurkat lymphocytes [21] and mouse BALB/c-3T3 fibroblast [22] [20,21,[24][25][26][27][28]. The unitary conductance of swellingactivated anion channels varies, but "intermediate conductance" (11-80 pS) channels appear to be the most common ones, described in many different cell types [9,10,[29][30][31].…”