VOLTAGE GATED CARDIAC POTASSIUM CHANNELS

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The long-term objective of my research is to study ion channel function and its relation to excitability, particularly in cardiac cells. In this work, I use a range of techniques and preparations. The current proposal is aimed at studying cardiac potassium channels in a newly developed system in which cloned channels are expressed. An expression system will be especially valuable because the study of cardiac K channels in native cells presents a series of technical difficulties. First the presence of more than ten potassium channels with diverse physiologies complicates detailed analysis of any individual potassium channel. Second, some are observed in less than 1/100 patches preventing reliable single channel analysis. Recent advances in molecular biology now provide unprecedented opportunities to clone and express individual channels. At Vanderbilt, seven potassium channels have been cloned from rat and human heart. These have been expressed in Xenopus oocytes but processing of such expressed channels may be different in mammalian cells. More recently, stable expression has been achieved in a mammalian cell line, mouse L-cells. The aims of this research project are to study physiological and pharmacological properties of cardiac potassium channels expressed individually in this new system, and to relate to results to channel function in native cells. The advantages of this expression system will be exploited to study in detail the voltage- and state-dependent interaction of drugs with these channels. Voltage clamp techniques, including whole cells, single channel and macropatch, will be used to analyze ion transfer, ion selectivity, gating properties, and drug sensitivity of these channels. Mathematical modelling will be used to provide a framework for further analyzing the experimental data, and to guide additional experiments. The properties of expressed channels win be compared to those of native channels further develop an understanding of the components which contribute to overall K current in cardiac cells. Potassium channels play an important role in controlling cardiac excitability and repolarization, and are the target for many available and investigational ('class III') antiarrhythmic agents. The information gained from this project will expand our knowledge of the function of these important channels, which may ultimately result in improved understanding of the mechanisms of arrhythmias and in the development of better antiarrhythmic drugs.