Abstract: AimTo investigate the role of endothelin-1 (ET-1) in the physiological and pathophysiological regulating mechanisms of voltage-gated K⁺ current (IK_V) inhibition in rat intrapulmonary arterial smooth muscle cells (PASMCs). MethodsSingle PASMCs were obtained with acute enzyme (collagnase plus papain) dispersing method. Using whole cell patch-clamp technique in freshly isolated rat PASMCs, the effect of ET-1 on voltage-gated K⁺ current was recorded. ResultsET-1 (1×10_-9 mol·L^-1) and the voltage-dependent K⁺ (K_V)-channel antagonist 4-aminopyridine (4AP), but not the Ca₂₊-activated K⁺-channel antagonist tetraethylammonium (TEA), caused membrane depolarization. The effect of ET-1 on membrane potential persisted in cells in which intracellular Ca₂₊ was buffered with 1,2-bis (2-aminophenoxy) ethane-n,n,n′,n′-tetraacetic acid (BAPTA). ET-1 (1×10_-9 mol·L^-1) caused a significant reversible inhibition of K_V current, which began 4.0 s after application of ET-1, was much earlier than the effect of membrane depolarization of PASMCs (15 s). ET-1 (1×10_-10 to 1×10_-7 mol·L^-1) caused a concentration-dependent inhibition of K⁺ current (+50 mV, from 136 to 40 pA/pF). The percent inhibition was 71% at 1×10_-7 mol·L^-1 (n=6). The effect of ET-1 (1×10_-9 mol·L^-1) on K⁺ current was weaker under conditions free of Ca₂₊ than containing Ca₂₊. At a test potential of +50 mV, free of Ca₂₊ conditions reduced the maximum inhibitory effect of ET-1 from 71% to 50%. ConclusionET-1 modulated pulmonary vascular reactivity by depolarizing membrane potential and inhibiting the K⁺ current of PASMCs. The effect of ET-1 on PASMCs membrane potential and the inhibition of K⁺ current were independent of Ca₂₊, but the inhibition of K⁺ current was much greater under conditions containing Ca₂₊ than free of Ca₂₊.