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.
