Characterisation of large-conductance calcium-activated potassium channels (BKCa) in human NT2-N cells

Large-conductance calcium-activated potassium (BKCa) channels were studied in inside-out patches of human NTERA2 neuronal cells (NT2-N). In symmetrical (140 mM) K+ the channel mean conductance was 265 pS, the current reversing at similar to 0 mV. It was selective (P-K/P-Na = 20:1) and blocked by internal paxilline and TEA. The open probability-voltage relationship for BKCa was fitted with a Boltzmann function, the V-1/2 being 76.3 mV, 33.6 mV and -14.1 mV at 0.1 mu M, 3.3 mu M and 10 mu M [Ca2+](i), respectively. The relationship between open probability and [Ca2+](i) was fitted by the Hill equation (Hill coefficient 2.7, half maximal activation at 2.0 mu M [Ca2+](i)). Open and closed dwell time histograms were fitted by the sum of two and three voltage-dependent exponentials, respectively. Increasing [Ca2+](i) produced both an increase in the longer open time constant and a decrease in the longest closed time constant, so increasing mean open time. Intracellular ATP evoked a concentration-dependent increase in NT2-N BKCa activity. At +40 mV half-maximum activation occurred at an [ATP](i) of 3 mM (30 nM [Ca2+](i)). ADP and GTP were less potent, and AMP-PNP was inactive. This is the first characterisation of a potassium channel in NT2-N cells showing that it is similar to the BKCa channel of other preparations. (c) 2006 Elsevier B.V. All rights reserved.