Voltage-gated Na+ currents (INaS) are usually not found in arterial smooth muscle. We enzymatically isolated myocytes from the media of left coronary arteries of heart transplant patients with ischemic cardiopathy. Using the whole-cell voltage-clamp technique (20 degrees C to 22 degrees C), we detected no INa in any of the freshly isolated myocytes. In contrast, when the cells were grown in culture, we could record a large INa. This INa was characterized by a biexponential decay comprising a fast inactivating and sustained components that could not be separated by their electrophysiological and pharmacological properties. INa activated at depolarizations positive to -50 mV, was maximal at 0 mV, and was available from relatively low resting membrane potentials (half-inactivation at -46 mV). INa was modulated by several ligands known to bind selectively at different sites of Na+ channels. It was blocked with high affinity by tetrodotoxin (IC50, approximately 10 nmol/L) and local anesthetics (bupivacaine and lidocaine; IC50, approximately 100 nmol/L) and by Cd2+ (IC50, approximately 300 mumol/L). INa was modulated by Na+ channel agonists such as toxin AsV from Anemonia sulcata and veratridine, which slowed current kinetics dramatically. In conclusion, human coronary myocytes in culture can express an atypical tetrodotoxin-sensitive INa with a large sustained component, which is expected to contribute to massive Na+ influx into these cells. Phenotypic modulation of the expression of this INa may be related to cell dedifferentiation and proliferation.