We have measured the kinetic and pharmacological properties of volume-activated Cl- currents (I(Cl,vol)) in endothelial cells, and tried to correlate them with those of the already described volume-activated current I(Cln). Both conductances show a similar permeability sequence for monovalent anions, and they are blocked by extracellular ATP. In the present report, we demonstrate by Western blot and RT-PCR that cultured endothelial cells from bovine pulmonary artery (CPAE) contain pI(Cln). The expression of this protein has been shown to be closely associated with the I(Cln) current. I(Cl,vol) showed however, in contrast with I(Cln), no striking inactivation at positive potentials. This property is also at variance with that of the volume-activated current related to MDR-1. Activation of I(Cl,vol) at potentials more negative than -80 mV was not time dependent, which excludes a major contribution of a ClC-2 related current. The antiviral nucleoside analogue AZT (3'-azido-3'-deoxythymidine) inhibited I(Cl,vol) by 21 ± 2.7% (n = 10), at a concentration of 100 μM. Another antiviral drug, acyclovir (ACV, 9-[(2-hydroxyethoxy)methyl]guanine) blocked I(Cl,vol) by 27 ± 6.2% at 100 μM (n = 11). Both blocking effects are much smaller than those reported for I(Cln). The phenol derivative gossypol, which blocks I(Cln)-related currents, efficiently inhibited I(Cl,vol) in CPAE cells (67 ± 2.1% at 1 μM, n = 7, K(I) = 0.4 μM). The presence of pI(Cln) in CPAE cells and the similar qualitative pharmacological profile of I(Cl,vol) and I(Cln) support the hypothesis that pI(Cln) is a good molecular candidate for I(Cl,vol) in endothelial cells. The discrepant kinetic properties may indicate that these time-dependent currents at high positive or negative potentials are not intrinsic properties of the channels, but are caused by time-dependent depletion/accumulation phenomena due to the large amplitudes of these currents.
ASJC Scopus subject areas
- Cell Biology