Abstract: AIM　To study the potassium currents in rat intrapulmonary artery smooth muscle cells(SMCs). METHODS　Using enzymatically isolated single SMCs and whole-cell patch-clamp techinique to record the potassium current. RESULTS　Current clamp recordings were made with perforated patch to assess the mean resting membrane potential which was -48±5 mV (n=9). Voltage clamp configurations were used to measure the membrane capacitance which was (27.9±1.2) pF(n=11). Outward potassium currents were evoked by using voltage ramps from -70 mV to +50 mV for a duration of 600 ms from a holding potential of -70 mV at the frequency of 0.1 Hz. The amplitude increased voltage-dependently which reached (359±31) pA(n=32) at +50 mV. The currents were fully depressed when the KCl in the electrode was substituted by 130 mmol.L^-1 CsCl. All the currents recorded with the external solution contained 1.2 mmol.L^-1 Ca²⁺ and the pipette solution contained a low concentration (1 mmol.L^-1) of ethylene glycol bis-(β-aminoethyl ether) N,N,N′,N′-tetraacetic acid(EGTA), while removal of extracellular Ca²⁺ and increase of the intracellular EGTA(from 1　mmol.L^-1 to 10　mmol.L^-1) reduced the current by 50%±1%. Specific calcium-activated potassium channel and delayed rectifier potassium channel blockers 5 mmol.L^-1 tetraethylammonium(TEA) and 4-aminopyridine(4-AP) can decrease the current from (12.52±1.08) pA/pF (control) to (6.75±1.54) pA/pF and from (13.99±1.11) pA/pF (control) to (9.38±2.36) pA/pF, respectively at +50 mV. CONCLUSION　The whole-cell potassium channel in the rat intrapulmonary artery smooth muscle cells consisted mainly of calcium-activated potassium currents and delayed rectifier potassium currents recorded by voltage-ramp patch-clamp technique.