Although the binding of neuroleptic drugs to dopamine receptors has been extensively studied, relatively little is known about drugs which might block the membrane ion channels through which the receptors give rise to a change in neuronal firing rate. This proposal aims to use patch-clamp electrophysiology to clarify the identity of the ion channels regulated by postsynaptic D1 and D2 dopamine receptors in rat corpus striatum, and to characterize the blockade of these single channel currents by channel blocking compounds. Freshly-dissociated corpus striatum neurons will be prepared from 31-45 day old Sprague-Dawley rats using enzymatic and mechanical dissociation methods, and used acutely for cell-attached patch recording. Such recording permit the measurement of channel currents with single-molecule resolution. Previous experiments using these methods have revealed the existence of an 85 pS potassium channel which appears to be activated by D2 receptors. These channels were blocked by nonomolar concentrations of quinine. Preliminary data suggest that there may be more than one type of channel modulated by dopamine receptors in these cells. Initially, experiments will focus on two specific issues. The first will be the identity of channels modulated respectively by D1 and D2 receptor subtypes. Subtype-selective agonists and antagonists will be used to study the pharmacology of channel activation, and various responses of striatal cells. Secondly, more extensive studies of quinine and otheer potential channel blocking agents will be made in order to compare dopamine-modulated channels with other known ion channels, and to develop a structure-activity relationship for blockade of these channels. Subsequently, responses in the nucleus accumbens will be compared with the striatum, and a variety of recording configurations and cell preparation methods will be added to the laboratory. The role of dopamine in psychosis and in drug abuse is incompletely understood. Preliminary data and the growing recognition of the diversity of potassium channels raise the possibility that some channel blocking agents may have some, but not all, of the properties of neuroleptics. This proposal is intended to acquire an understanding at the basic science level of the ionic transduction mechanisms of dopamine receptors, as a necessary first step to taking a rational approach to studying these channels as possible drug targets.
