KCNN4 and nonpapillary renal cell carcinoma: In addition to KCa3.1, we identified also the distantly related, voltage- and Ca2+-activated KCa1.1 channel as a differentially expressed channel in the two tumor types (3-fold higher mRNA expression and presence of functional KCa1.1 currents in ccRCC but not in oncocytoma) and between healthy and tumor tissue of the same kidney.