Voltage-gated sodium channels in cardiac microvascular endothelial cells

Macrovascular endothelial cells express voltage-gated K⁺ channels but appear to lack Ca²⁺ and Na⁺ channels. The goal of this study was to begin characterizing ion channels in cardiac microvascular endothelial cells (CMECs). CMECs were isolated from rat ventricular muscle and studied between days 1-5 in culture. Differential uptake of flourescently-labeled acetylated LDL indicated that the primary culture contained > 90 % CMECs. Membrane currents were measured using the whole-cell arrangement of the patch clamp technique. Cells were dialyzed with internal Cs⁺ to block the outward K⁺ currents. Voltage steps positive to -30 mV resulted in the activation of inward Na⁺currents (I^Na). In 10 cells analyzed, the peak I_Na was 2.5 pA/pF and the current inactivated with a V_1/2 of -45 mV. I_Na was eliminated by replacement of external sodium with N-methylglucamine and was blocked by tetrodotoxin (K_d = 3 nM). Voltage-gated Na⁺ channels may promote electrical conduction between capillaries and arterioles following membrane (Figure Presented) depolarization.