We have characterized two different types of Cl− currents in calf pulmonary artery endothelial (CPAE) cells by using a combined patch-clamp and Fura-2 microfluorescence technique to measure simultaneously ionic currents and the intracellular Ca2+ concentration, [Ca2+]i. Exposure of CPAE cells to 28% hypotonic solution induces cell swelling without a change in membrane capacitance and [Ca2+]i, and concomitantly activates a current. This current, ICl, vol, is closely correlated with the changes in cell volume and shows a modest outward rectification. It slowly inactivates at potentials more positive than +60 mV but is time- and voltage-independent at other potentials. Increase in [Ca2+]i by different maneuvers, such as application of vasoactive agonists (ATP), ionomycin, or loading of the cells directly with Ca2+ also activates a Cl− current, IclcaThis current slowly activates at positive potentials, inactivates quickly at negative potentials and shows strong outward rectification. A time-independent component of the current activated by elevation of [Ca2+]i alone can be inhibited by cell shrinking by exposing the cells to hypertonic solution, indicating that an increase in [Ca2+]i also co-activates IClvolForskolin or cAMP never activated a current in CPAE cells, which indicates the lack of cAMP-activated channels in these cells. There is also no evidence for the existence of voltage-gated C− channels in resting, nonstimulated cells. Challenging a cell with elevated [Ca2+]i and hypotonic solutions activated IClvol on top of IClca, suggesting that ICl Ca and IClvol are different channels. We conclude that CPAE cells do not express voltage-gated (CIC-type) or cAMP-gated (CFTR-type) Cl− channels, but activate large Cl− currents after volume (mechanical?) or chemical (Ca2+) stimulation.
- Chloride channels
- Patch clamp
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine