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

Abstract

Large-conductance calcium-activated potassium (BK Ca) 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 ∼ 0 mV. It was selective ( P K / P Na = 20:1) and blocked by internal paxilline and TEA. The open probability–voltage relationship for BK Ca was fitted with a Boltzmann function, the V ½ being 76.3 mV, 33.6 mV and − 14.1 mV at 0.1 μM, 3.3 μM and 10 μM [Ca 2+] i , respectively. The relationship between open probability and [Ca 2+] i was fitted by the Hill equation (Hill coefficient 2.7, half maximal activation at 2.0 μM [Ca 2+] i ). Open and closed dwell time histograms were fitted by the sum of two and three voltage-dependent exponentials, respectively. Increasing [Ca 2+] 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 BK Ca activity. At + 40 mV half-maximum activation occurred at an [ATP] i of 3 mM (30 nM [Ca 2+] 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 BK Ca channel of other preparations.