[Study on delayed rectifier K+ current of rabbit vascular smooth muscle cells and comparison with cloned Kv1.5...

Whole cell patch-clamp recording techniques were used to compare the electrophysiological properties between delayed rectifier K+ current of rabbit vascular smooth muscle cell (VSMC) and the cloned Kv1.5 channel. When VSMC is clamped at -40 mV, depolarizing the membrane potential at increasing steps of 10 mV could evoke a series of outward potassium currents without any deactivation. The V1/2 of the activation curve was 27.2 mV. The currents decrease obviously after adding 100 mmol/L TEA or 1 mmol/L 4AP in the perfusate. When the concentration of extracellular Ca2+ was decreased from 1.5 mmol/L to 0.5 or 0 mmol/L, the currents did not show much change, while in HBK7 (cloned Kv1.5 channel cell) held at -80 mV, similar steparise depolarization could also produce a series of outward potassium currents without any deactivation decayed. V1/2 of the activation was 0.8 mV. 4AP inhibited the cloned channel current with IC50 of 7.3 mmol/L, showing neither frequency- or use-dependence. TEA (30, 100 and 300 mmol/L) reduced the current by 28.6%, 37.4% and 46.3% respectively. Quinidine (0.1 and 1 mmol/L) decreased it by 29.7% and 37.4%. These results show what we have recorded in isolated rabbit vascular smooth muscle cells is the delayed rectifier potassium currents which are different in electrophysiological and pharmacological properties from those of cloned Kv1.5 channel current.