Kv channels represent new important targets for the control of cancer growth and a better understanding of their regulating pathways in cancer cells is necessary to develop therapeutic strategies. In this study, we have addressed the putative modulation of Kv by MAP kinases through a pharmacological approach. We have found that the commonly used JNK inhibitor SP600125 strongly inhibits Kv channels through a JNK-independent pathway, likely interacting directly with the channels at the external side of the membrane. Our results indicate that the use of this compound may produce misleading conclusions for the role of JNK in cell cycle.