Human saphenous vein endothelial cells express a tetrodotoxin- resistant, voltage-gated sodium current

Whole-cell patch-clamp electrophysiological investigation of endothelial cells cultured from human saphenous vein (HSVECs) has identified a voltage- gated Na+ current with a mean peak magnitude of -595 ± 49 pA (n = 75). This current was inhibited by tetrodotoxin (TTX) in a concentration-dependent manner, with an IC50 value of 4.7 µM, suggesting that it was of the TTX- resistant subtype. An antibody directed against the highly conserved intracellular linker region between domains III and IV of known Na+ channel a-subunits was able to retard current inactivation when applied intracellularly. This antibody identified a 245-kDa protein from membrane lysates on Western blotting and positively immunolabeled both cultured HSVECs and intact venous endothelium. HSVECs were also shown by reverse transcription-polymerase chain reaction to contain transcripts of the hH1 sodium channel gene. The expression of Na+ channels by HSVECs was shown using electrophysiology and cell-based enzyme-linked immunosorbent assay to be dependent on the concentration and source of human serum. Together, these results suggest that TTX-resistant Na+ channels of the hill isoform are expressed in human saphenous vein endothelium and that the presence of these channels is controlled by a serum factor.