Prolonged exposure to decreased oxygen tension causes contraction and proliferation of pulmonary arterial smooth muscle cells (PASMCs) and pulmonary hypertension. Hypoxia-induced inhibition of voltage-gated K⁺ (K_v) channels may contribute to the development of pulmonary hypertension by increasing intracellular calcium concentration ([Ca²⁺]_i). The peptide endothelin-1 (ET-1) has been implicated in the development of pulmonary hypertension and acutely decreases K_v channel activity. ET-1 also activates several transcription factors, although whether ET-1 alters K_V channel expression is unclear. The hypoxic induction of ET-1 is regulated by the transcription factor hypoxia-inducible factor-1 (HIF-1), which we demonstrated to regulate hypoxia-induced decreases in K_V channel activity. In this study, we tested the hypothesis that HIF-1-dependent increases in ET-1 lead to decreased K_v channel expression and subsequent elevation in [Ca²⁺]_i. Resting [Ca²⁺]_i and K_v channel expression were measured in cells exposed to control (18% O₂, 5% CO₂) and hypoxic (4% O₂, 5% CO₂) conditions. Hypoxia caused a decrease in expression of K_v1.5 and K_v2.1 and a significant increase in resting [Ca²⁺]_i. The increase in [Ca²⁺]_i was reduced by nifedipine, an inhibitor of voltage-dependent calcium channels, and removal of extracellular calcium. Treatment with BQ-123, an ET-1 receptor inhibitor, prevented the hypoxia-induced decrease in K_v channel expression and blunted the hypoxia-induced increase in [Ca²⁺]_i in PASMCs, whereas ET-1 mimicked the effects of hypoxia. Both hypoxia and overexpression of HIF-1 under normoxic conditions increased ET-1 expression. These results suggest that the inhibition of K_v channel expression and rise in [Ca²⁺]_i during chronic hypoxia may be the result of HIF-1-dependent induction of ET-1.