Renal cells transformed with SV40 contain a high-conductance calcium-insensitive potassium channel

The inside-out variant of the patch-clamp technique was used to investigate the properties of a K+ channel occurring in 20% of patches from two renal cell lines transformed with the wild-type simian virus 40 (SV40) (Vandewalle et al. J. Cell. Physiol. 141: 203-221, 1989). This channel was practically absent from the primary cultures of renal cortical cells from which the cell lines were originally derived. With identical K(+)-rich solutions on both sides of the membrane patch, the channel showed an inwardly rectifying current-voltage relationship with unit conductances of 151.8 +/- 4.8 pS at negative and 86.4 +/- 5.9 pS at positive voltages (n = 18). When K+ in the bath was replaced by Na+, a mean reversal potential of 57.0 +/- 5.2 mV (n = 6) was observed from which a K(+)-to-Na+ permeability ratio of 13 was calculated. The channel was insensitive to internal Ca2+ and was blocked by internal Ba2+. No clear dependence on voltage was apparent. This channel bears no resemblance to any epithelial K+ channel and may be a novel type of K+ channel. Its occurrence in two transformed cell lines with quite distinct phenotypes, one of proximal cells (RC.SV1) and the other of thick ascending limb cells (RC.SV2), suggests that transformation by SV40 might be responsible for its appearance.