Voltage gated potassium channels of cultured rat central neurons.

Whole cell and single channel patch clamp recording were used to study the properties of two types of voltage gated potassium channels in rat neurons. Neurons were dissociated from either the locus coeruleus or hippocampus of neonatal rats and grown in primary cell culture for 6 to 17 days before recording. Cultured neurons from both these brain areas were found to express whole cell A-currents and delayed rectifier currents, similar to those seen in other neurons. The conductance of single A-current channels in locus coeruleus neurons was 14.8pS, although this declined at positive membrane potentials. This reduction in unitary amplitude was shown to be due to voltage dependent block of the channel by intracellular magnesium and sodium ions. The Kd values of the blocking reactions at 0mV membrane potential were 15.7mM for magnesium and 76.0mM for sodium, the Kd of each block decreasing with increasing membrane depolarisation. The conductance of single delayed rectifier channels in hippocampal neurons was 18.4pS. Gating of this channel could be explained by a model in which the channel had one open state, four closed states and three inactivated states. This scheme was not consistent with a Hodgkin-Huxley model of voltage dependent gating, but instead favoured a model whereby gating occurred in a cooperative manner. Gating could be altered by changing the permeant ion from potassium to the less permeable rubidium; this had the effect of specifically slowing all channel closing rate constants. The rubidium permeability of this channel was 75% of the potassium permeability. External tetraethyl ammonium ions blocked delayed rectifier channels at two independent sites, each block having different kinetic properties. The Kd of the kinetically faster block was 53.4?M, whilst that of the slower block was estimated to be between 400 and 800?M