Intermediate conductance Ca2+-activated potassium channel (KCa3.1) in the inner mitochondrial membrane of human colon cancer cells.

Patch-clamp, cell attached recordings from mitoplasts isolated from human colon carcinoma 116 cells has allowed the identification and characterization of the intermediate conductance Ca(2+)-activated K(+)-selective channel K(Ca)3.1, previously studied only in the plasma membrane of various cell types. The identity of this channel has been established by its unitary conductance, inward rectification of the single-channel I-V relationship, calcium dependence of the open probability, and sensitivity to the K(Ca)3.1 channel blockers clotrimazole (10 and 100 nM) and TRAM-34 (10 and 100 nM). The properties of the KCa3.1 channels assessed in mitoplasts was similar to the properties of the same channel found on the plasmamembrane of the same cells. Its localisation in the inner membrane of mitochondria is indicated by Western blots of subcellular fractions, by recording of its activity in mitochondria made fluorescent by a mitochondria-targeted fluorescent protein and by the co-presence of channels considered to be markers of the inner membrane. Moderate increases of mitochondrial matrix [Ca(2+)] will cause mtK(Ca)3.1 opening, thus linking inner membrane K(+) permeability and transmembrane potential to Ca(2+) signalling. Our observations lead to the conclusion that the Ca2+-activated, K+-selective KCa3.1 channel is present in the inner membrane of mitochondria isolated from HCT116 cells. Further investigation is needed to establish the physiological significance of our finding.