Calcium-activated potassium channels in the endothelium of intact rat aorta

A novel mechanosensitive cationic channel from the endothelium of rat aorta

1. Single channel currents were recorded from the lumenal surface of endothelium of excised intact rat aorta using the patch clamp technique. 2. The majority of cell-attached and inside-out patches contained cationic channels with an equal permeability to Na+ and K+. Positive pressure applied through the pipette reversibly increased their open probability, whereas negative pressure reversibly decreased it. The dependence of the channel activity on pressure was sigmoidal in all tested patches. 3. The slope conductance of the channel for inward current was 33.9 +/- 2.1 pS in a nominally Ca(2+)-free extracellular solution. With 1 mM CaCl2 in the extracellular solution, the channel conductance for inward current was reduced to 21.2 +/- 2.3 pS. In isotonic CaCl2 solution, the slope conductance of the channel was 5.9 +/- 1.3 pS. The ionic permeability ratio was PCa: PNa: PK = 3.5:1:1. 4. Gadolinium and lanthanum at a concentration of 10 microM did not affect the channels, but at higher concentrations (> or = 100 microM) reduced inward currents through the channels. 5. The mechanosensitive channel reported here is different in its gating mechanism and pharmacology from stretch-activated channels described previously. This channel may be involved in mechanotransduction of haemodynamic stimuli in endothelium.

Ion channels in vascular endothelium

The functional impact of ion channels in vascular endothelial cells (ECs) is still a matter of controversy. This review describes different types of ion channels in ECs and their role in electrogenesis, Ca2+ signaling, vessel permeability, cell-cell communication, mechano-sensor functions, and pH and volume regulation. One major function of ion channels in ECs is the control of Ca2+ influx either by a direct modulation of the Ca2+ influx pathway or by indirect modulation of K+ and Cl- channels, thereby clamping the membrane at a sufficiently negative potential to provide the necessary driving force for a sustained Ca2+ influx. We discuss various mechanisms of Ca2+ influx stimulation: those that activate nonselective, Ca(2+)-permeable cation channels or those that activate Ca(2+)-selective channels, exclusively or partially operated by the filling state of intracellular Ca2+ stores. We also describe the role of various Ca(2+)- and shear stress-activated K+ channels and different types of Cl- channels for the regulation of the membrane potential.