Classical conditioning of the rabbit nictitating membrane response involves changes in both synaptic and intrinsic membrane properties of Purkinje cell dendrites in the cerebellar cortex and pharmacological evidence suggests that a 4-aminopyridine (4AP) sensitive potassium channel underlies the membrane changes. We characterized IA currents in adult, rabbit cerebellar Purkinje cells to determine whether IA might be the target channel involved in learning. Standard whole-cell voltage clamp of Purkinje cell somas and dendrites revealed a fast activating and inactivating current with half maximal activation at -27.08±3.48mV and -25.51±1.15mV in soma and dendrites, respectively, half maximal inactivation at -58.91±2.34 mV and -49.90±2.58mV and a recovery time constant of 22.81±1.92ms and 16.60±4.26ms. More importantly, there was an overlap of activation and incomplete inactivation at potentials from -60mV to -40mV suggesting a “window” current that was responsible for subthreshold variations of membrane potential and might underlie conditioning-specific increases in Purkinje cell excitability.

Figure shows the voltage dependence of both activation and inactivation of transient potassium currents in rabbit cerebellar Purkinje cells thought to be involved in learning and memory. (Click to Enlarge)