Ca2+‐Inactivated K+ Current is Modulated by Endothelin‐1 in B‐16 Murine Melanoma Cells

It is well established that endothelin‐1 (ET‐1) plays a role in differentiation and proliferation in a variety of cells such as fibroblasts and human melanoma cells via a receptor‐mediated mechanism. However, whether ET‐1 modulates ion channel activity in these cell types is still unknown. In this report, we recorded the voltage‐dependent outward K⁺ current in cultured B16 melanoma cells using the patch‐clamp technique. Biophysical and pharmacological properties of the K⁺ current, and the effect of ET‐1 on the K⁺ current were investigated. When cells were loaded with a Ca²⁺‐chelating agent (EGTA or BAPTA), the K⁺ current amplitude gradually increased with time after establishment of the whole cell configuration. Replacement of Ca²⁺ with Co²⁺ in the extracellular medium caused no significant modulation of the K⁺ current amplitude. Addition of BaCl₂ or quinidine to the extracellular solution reduced the K⁺ current amplitude, whereas the K⁺ current was insensitive to tetraethylammonium. ET‐1 (10 nM) reversibly decreased the K⁺ current amplitude and accelerated the decay of the K⁺ current. The ET‐1‐induced inhibitory effect displayed no desensitization following repeated ET‐1 application. Pretreatment with pertussis toxin (PTX) or perfusion of cells with the protein kinase C (PKC) inhibitor H‐7 abolished the inhibitory effect of ET‐1 on the K⁺ current. We conclude that the outward K⁺ current recorded in murine B‐16 melanoma cells represents a Ca²⁺‐inactivated K⁺ current, and that the inhibitory effect of ET‐1 on the K⁺ current may reveal a novel mechanism to control the differentiation and proliferation of melanoma cells.