Two Types of Voltage-dependent Outward Potassium Currents in Smooth Muscle Cells of Rabbit Basilar Atery

Two Types of Voltage-dependent Outward Potassium Currents in Smooth Muscle Cells of Rabbit Basilar Atery

<P> We have investigated the two types of voltage-dependent outward potassium (K) currents, i.e. delayed rectifier K current (I<SUB>K(V)</SUB>) and A-like transient outward K current (I<SUB>to</SUB>) with patch-clamp technique in single smooth muscle cells (SMCs) isolated from rabbit basilar artery, and investigated the characteristics of them. The time-courses of activation were well fitted by exponential function raised to second power (n<SUP>2</SUP>) in I<SUB>K(v)</SUB> and fourth power (n<SUP>4</SUP>) in I<SUB>to</SUB>. The activation, inactivation and recovery time courses of I<SUB>to</SUB> were much faster than that of I<SUB>K(V)</SUB>. The steady-state activation and inactivation of I<SUB>K(V)</SUB> was at the more hyperpolarized range than that of I<SUB>to</SUB> contrary to the reports in other vascular SMCs. Tetraethylammonium chloride (TEA; 10 mM) markedly inhibited I<SUB>K(V)</SUB> but little affected I<SUB>to</SUB>. 4-Aminopyridine (4-AP) had similar inhibitory potency on both currents. While a low concentration of Cd<SUP>2+</SUP> (0.5 mM) shifted the current- voltage relationship of I<SUB>to</SUB> to the positive direction without change of maximum conductance, Cd<SUP>2+</SUP> did not cause any appreciable change for I<SUB>K(V)</SUB>.