Background nonselective cationic current and the resting membrane potential in rabbit aorta endothelial cells

The ion channel conductances that regulate the membrane potential was inves tigated by using a perforated patch-clamp technique in rabbit aorta endothe lial cells (RAECs). The whole-cell current/voltage (I-V) relation showed a slight outward rectification under physiological ionic conditions. The rest ing membrane potential was -23.3+/- 1.1 mV (mean+/-SEM, n=19). The slope co nductances at the potentials of -80 and 50mV were 31.0+/-4.0 and 62.8+/-7.1 pS pF(-1), respectively (n=15). Changes in the extracellular and intracell ular Cl- concentrations did not affect the reversal potential on I-V curves . The background nonselective cationic (NSC) current was isolated after the K+ current was suppressed. The relative permeabilities calculated from the changes in reversal potentials using the constant-field theory were P-K: P -Cs: P-Na: P-Li = 1:0.87:0.40:0.27 and P-Cs: P-Ca = 1:0.21. Increases in th e external Ca2+ decreased the background NSC current in a dose-dependent ma nner. The concentration for half block by Ca2+ was 1.1+/-0.3 mM (n=7). Thro ugh the continuous recording of the membrane potential in a current-clamp m ode, it was found that the background NSC conductance is the major determin ant of resting membrane potential. Taken together, it could be concluded th at the background NSC channels function as the major determinant for the re sting membrane potential and can be responsible for the background Ca2+ ent ry pathway in freshly isolated RAECs.