Electrophysiological Methods to Explore the Function of Monoamine Transporters

In this chapter we will show how electrophysiological recordings were used to gain insights into the transport kinetics and pharmacology of monoamine transporters (MATs). We will discuss data obtained from whole cell patch clamp recordings that allow for real time monitoring of MAT function. A notable property of MATs is that they carry so-called uncoupled currents. We will begin this chapter by reviewing the experimental evidence that has led to the conclusion that the currents carried by MATs are largely uncoupled and, therefore, not directly related to substrate transport. We will discuss how this has made it difficult to understand the operation of MATs. We will also explain why the existence of these currents has led to the proposition that MATs do not operate by alternate access but rather by a single file diffusion mechanism. However, we will show that ultimately the uncoupled currents carried by MATs can be most parsimoniously explained within the framework of the alternate access mechanism. We will review the existing evidence that MATs, like most other transporters, undergo a cycle during which they visit outward and inward-facing conformations (i.e., the transport cycle). We will outline what we have learned about the transport cycle of MATs from electrophysiological recordings. Thereafter, we will describe how electrophysiological recordings can be utilized to understand how drugs that target MATs affect their operation. To this end, we will discuss the binding modes of three different MAT ligands: (i) amphetamines, (ii) ibogaine, and (iii) zinc.