The recording of action potential currents as an assessment for drug actions on excitable cells

The use of the cell-attached patch clamp configuration to record action potential currents is shown to have utility in the testing for drug actions on ion channels in excitable cell membrane. A patch pipette was used to isolate a small patch of cell membrane on cultured hippocampal or hypothalamic neurons and spontaneous R-C coupled action potential currents, with well-defined Na+ and K+ components, were recorded. The addition of several potassium channel-blocking drugs to the bath solution completely abolished the after-hyperpolarization phase of the action potential currents while preserving the sodium spike. These drugs have previously been shown to block a calcium-dependent potassium channel in cultured hippocampal neurons, a channel that is responsible for the late slow after-hyperpolarization macroscopic current recorded in these cells. The addition of tetrodotoxin to the bath solution eliminated the R-C coupled currents. The novel approach of using the recording of action potential currents to assess drug actions on ion channels would be expected to be applicable to a variety of excitable cells.