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

The ion channel conductances that regulate the membrane potential was investigated by using a perforated patch-clamp technique in rabbit aorta endothelial cells (RAECs). The whole-cell current/voltage (I-V) relation showed a slight outward rectification under physiological ionic conditions. The resting membrane potential was -23.3±1.1 mV (mean±SEM, n=19). The slope conductances at the potentials of -80 and 50 mV were 31.0±4.0 and 62.8±7.1 pS pF^-1, respectively (n=15). Changes in the extracellular and intracellular 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 the external Ca²⁺ decreased the background NSC current in a dose-dependent manner. The concentration for half block by Ca²⁺ was 1.1±0.3 mM (n=7). Through the continuous recording of the membrane potential in a current-clamp mode, it was found that the background NSC conductance is the major determinant of resting membrane potential. Taken together, it could be concluded that the background NSC channels function as the major determinant for the resting membrane potential and can be responsible for the background Ca²⁺ entry pathway in freshly isolated RAECs.