STUDY ON POTASSIUM CHANNELS OF RAT INTRAPULMONARY ARTERY SMOOTH MUSCLE CELLS

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.