The human embryonic kidney cells (HEK-293) have been widely used as one mammalian expression system in the study of voltage-gated K+ (Kv) channels. Understanding the endogenous Kv channels in these cells is the prerequisite for the characterization of the heterogeneously expressed Kv channels in these cells. In the present study we screened the transcriptional expression of different Kv genes in HEK-293 cells using reverse transcribed DNApolymerase chain reaction (RT-PCR) method. Among 16 Kv genes examined in native HEK-293 cells 10 Kv genes were reproducibly amplified, including those Kv a subunits encoding for the delayed rectifier (IK) [Kv1.1, Kv1.2, Kv1.3, Kv1.6, and Kv3.1], and for the transient outward Kv channels (IA) [Kv1.4, Kv3.3, Kv3.4, and Kv4.1] as well as a Kvbeta2 subunit. The whole-cell outward rectifier IK currents in the native HEK-293 cells were recorded (203 +/- 13 pA at +30 mV, n = 82) with the patch-clamp technique. In about 42% of the examined cells, IA coexisted with IK currents. IK currents were inhibited by tetraethylammonium chloride (TEA) at 1 and 10 mM by 39.5 and 48.4%, respectively. A 39.6% inhibition of IK currents was also observed in the presence of4-aminopyridine (4-AP, 5 mM). Interestingly, both TEAand 4-AP also inhibited IA currents. 4-acelamido-4'-isothiocyanalostilbene-2, 2'-disulfonic acid (1 mM), a Cl- channel blocker, had no effect on the endogenous outward currents. We concluded that multiple endogenous Kv genes were expressed in native HEK-293 cells, which possessed significant endogenous IK and IA currents with unique pharmacological properties.