Membrane currents of cultured rat neostriatal neurones

This thesis describes an electrophysiological study of cultured neurones from the rat neostriatum using the patch clamp technique. The aims of the study were to investigate the voltage-activated currents which play a role in determining the activity patterns of these neurones and to examine individual K+ channels responsible for the resting conductance. The neurones displayed highly negative resting membrane potentials ([approximately equal] -90 mV) and a "leak" conductance which showed inward rectification. They expressed an assortment of voltage- activated macroscopic currents. Transient outward currents, which activated rapidly on depolarization, were especially prominent. Such currents were progressively inactivated by subthreshold depolarization. The three most prevalent potassium-conductive channels in these neurones have been identified and partially characterized. Comparable channels were observed in cell-attached and outside- out configurations. In cell-attached patches, small and intermediate conductance channels (27 pS and 130 pS in symmetrical 14 0 mM K+) were active over a wide range of potentials including the resting membrane potential. Large conductance "maxi" channels (200-275 pS) were also present and were strongly activated by depolarization. Maxi channel activity varied considerably from patch to patch, sometimes being appreciable at the resting potential. Activity could often be permanently elevated by depolarization. Such a "priming" effect on maxi channel activity has not previously been reported. The novel small and intermediate channels were considerably active at the resting potential. It has been estimated that each channel type would contributed, on average, 2-3 nS to the resting conductance under physiological conditions. The resting input conductance measured in whole cell experiments was a similar order of magnitude (mean~ 3 nS). Thus, these channels could account for the bulk of the resting conductance. The possible roles of the whole cell and single channel k+ currents records in this study, and the consequences of their activation with regard to cell excitability are discussed.