Antiproliferative effects of neuroprotective drugs targeting big Ca2+-activated K+ (BK) channel in the undifferentiated neuroblastoma cells

The big Ca2+-activated K+ (BK) channel has a role in regulating cell viability and survival in a variety of cells. The effects of drugs targeting the BK channels in neuronal and smooth muscle tissues in the human SH-SY5Y cell and mouse Neuro2A undifferentiated neuroblastoma cells have never been investigated. The expression/activity of BK channel subunits and the effects of the BK channel openers: acetazolamide (ACTZ) (10-7 - 2 × 10-4 M), resveratrol (RESV) (10-7 - 2 × 10-4 M), dichlorphenamide (DCP) (10-12 - 2 × 10-4 M), bendroflumethiazide (BFT) (10-9 - 10-5 M) and riluzole (RIL) (10-6 - 10-4 M) were evaluated by real time-polymerase chain reaction (RT-PCR)/patch-clamp experiments in SH-SY5Y cells and Neuro2a. Cell proliferation was evaluated by cell-dehydrogenase activity (CCK8-assay), cell impedentiometric (Scepter-counter) and clonogenic assays. An elevated expression/activity of the hslo1-BK channel subunit was observed in the SH-SY5Y, while a low expression/activity of this subunit was found in the Neuro2a. Tetraethylammonium (TEA) (1 - 5 x 10-3) and iberiotoxin (IbTX) (10-9 - 6 × 10-7 M) caused a marked inhibition of the whole-cell K+-currents in SH-SY5Y. A mild inhibition of the K+-currents was found in Neuro2a with these compounds. The application of ACTZ, DCP, RESV and BFT to the patches failed to activate the K+-currents but rather reduced it. The rank order of efficacy of the drugs as K+-current inhibitors at +30 mV (Vm) was: TEA > RESV ≥ IbTX > DCP > ACTZ > BFT. RESV and IbTX irreversibly reduced the K+-currents and the cell number in the enzymatic, clonogenic and impedentiometric assays with RESV being more effective than IbTX. TEA reversibly reduced the K+-currents without affecting cell proliferation. Whereas, RIL potentiated the BK current and reduced cell-dehydrogenases activity with no changes in the cell morphology and number. The observed irreversible BK channel-blocking action exerted by RESV and IbTX can be associated with anti-proliferative effects in cells overexpressing hslo1-BK channel subunit. This can be an additional mechanism contributing to the cytotoxic action of RESV in SH-SY5Y cells.