The long-term objectives of this work are to understand the functional properties and physiological roles of potassium channels derived from the extended gene family known as eag. This proposal focuses on one member of this family, h-erg, which was isolated from the human hippocampus. In contrast to their outwardly-rectifying relatives in the eag family, h-erg ion channels are inward rectifiers, conducting potassium current into the cell when the membrane is hyperpolarized. Like all inward rectifiers, the voltages at which activation occurs depends on the driving force on potassium ions, as though the potassium ions themselves dislodge an internal blocking particle from the conduction pathway. The gating of h- erg channels is complex, however. Activation of the current by a hyperpolarization requires a depolarizing prepulse. The prepulse voltage apparently regulates the availability of channels for activation during the subsequent hyperpolarization. This process is characterized by a voltage dependence that is similar to that of activation of the outwardly- rectifying channels with which h-erg shares significant structural similarity. Thus, the gating of these channels encompasses properties of both inward and outward rectifiers. The first two specific aims are to derive rates for transitions of each gating process from macroscopic current analysis and to develop a model that accounts for the observed complexities. The third specific aim examines the mechanism of inward rectification, to determine whether it arises from (1) an extrinsic blocking particle, such as Mg ions, (2) a polypeptide blocking mechanism that is intrinsic tot he channel itself, or (3) conformational changes in the pore. The fourth specific aim involves mutagenesis studies which take advantage of the considerable sequence homology between h-erg and other channels in the eag family to map functional differences to discrete domains of the channel polypeptide. There is great potential for clinical advances in basic studies of new types of channels such as the inward rectifiers, which are highly expressed in the heart and nervous system. Ion channels are important targets for therapeutic drugs, and effective drug design requires a detailed understanding of channel structure and function. In addition, since a growing number of diseases have been ascribed to defects in ion channel function, inward rectifier channels represent potential disease loci and targets from gene therapy. With these studies we seek to advance our understanding of the basic properties of h-erg and related channels as the groundwork for progress in health-related applications.
