Patch-clamp studies of macroscopic and single-channel currents in mouse neuroblastoma cells.

Cells from the clonal cell line N1E115, a mouse tumour of sympathetic origin, differentiate both morphologically and electrophysiologically when cultured in medium containing dimethylsulphoxide. This technique was used to obtain cells for electrophysiological recording. Macroscopic currents were measured using the whole-cell patch-clamp technique and two currents, one thought to be carried mainly by sodium ions and one mainly by potassium ions, were identified. The kinetics of the potassium current, which are voltage dependent, suggested that this was a delayed rectifier. A single-channel current which was selective for potassium ions was recorded using the cell-attached patch-clamp recording technique. The channel was thought to be the unitary current correlate of the macroscopic potassium current on the basis of its activation kinetics. The channel was shown to have two open states of different conductance, one having approximately two-thirds the conductance of the other. The single-channel kinetics were measured and it was shown that the open time distribution of the channel, the latency to its first opening after a voltage step and the relative times spent in each of the two open states are voltage dependent. The amplitude of these currents was reduced by application of tetraethylammonium ions to the extracellular face of the membrane patch and the concentration- and voltage-dependence of this block were investigated. Two further unitary currents were identified using the excised patch-clamp recording technique: a calcium-activated non-selective cation current and a calcium-activated potassium current. The conductance and voltage-dependence of both currents were investigated.