Pharmacological and molecular characterisation of SK3 channels in the TE671 human medulloblastoma cell line

The expression of the small conductance calcium-activated potassium channels SK1, SK2 and SK3 was investigated in the TE671 human medulloblastoma cell line using RT-PCR and transcripts were detected only for SK3. Immunodetection experiments confirmed this result, demonstrating the presence of the SK3 protein. This potassium channel was characterised in TE671 cells using whole-cell patch-clamp recordings. Voltage steps to -100 mV from a holding potential of 0 mV in equimolar 140 mM intra- and extracellular K (K elicited an inward current. The reversal potential of this current shifted 56.6 mV per 10-fold increase in K-out(+) thus suggesting K+ selectivity. This current was dependent on the concentration of Ca-in(2+) with an EC50 of 104.2 nM. A pharmacological characterisation of this current revealed that it was not blocked by 1 muM charybdotoxin (ChTX), 0.3 muM iberiotoxin (IbTX) or 10 muM clotrimazole (CLT) and only modestly inhibited (<50%) by 30 nM scyllatoxin (ScTX), 200 muM dequalinium chloride (Deq) or 300 muM d-tubocurarine (d-TC). The non-selective SK blocker d-TC blocked the current with an IC50 of 43.2 muM while apamin blocked the current to a much greater extent (87.8% at muM) with an IC50 of 4.3 nM. Furthermore, the current was significantly increased ( 132.6-5.2%, n =7) by 500 muM 1-ethyl-2-benzimidazolinone (EBIO). Collectively, these data demonstrate the presence of an endogenous SK3 channel ill human TE671 cells. (C) 2002 Elsevier Science B.V. All rights reserved.