Background: Ion channels in normal cardiac tissue reside in specific locations on the plasma membrane of heart cells. Their proper functioning is critical for the electrical activity that coordinates each heartbeat as well as determining the strength of contraction of heart muscle. Abnormal regulation of cardiac ion channels is part of the pathophysiology of heart failure (550,000 new U.S. cases and 53,000 deaths annually) and sudden cardiac death (300,000 annual U.S. cases). However, little is known about the molecular mechanisms by which ion channel positioning, and hence ion channel function, are regulated in normal physiology and disrupted in cardiac disease.
Major Goals: (i) Determine the molecular mechanisms by which cardiac ion channels are localized to specialized subregions on the ventricular cell plasma membrane. (ii) Understand how cardiac ischemia disrupts ion channel expression and function.
Dynamic Ion channel Membrane Expression: The cardiac ventricular cell surface membrane, like all plasma membranes, is a lipid bilayer in which membrane proteins can move laterally by diffusion. However, ion channel lateral diffusion may be limited by their multimeric structure and linkage to adjacent anchoring proteins. Ion channel placement is likely due to targeting to specific regions on the membrane from general cytoplasmic sources. We are interested in the mechanisms by which ion channels traffick to subregions of surface membrane and the mobility of the channels once in the membrane.
Channel Regulation during Ischemia: Previous work has determined that the microtubule cytoskeleton targets cardiac gap junctions to specific locations on the cardiac myocyte by interaction between microtubule plus-end tracking protein (+TIP) EB1 and the membrane cadherin based adherence junction complex. Our hypothesis is that ischemia affects EB1 and the adherens junction, thereby resulting in improper gap junction placement.
Live Cell Imaging of Membrane Channels: Aside from standard cell biology and biochemical techniques, the laboratory performs live cell microscopy using widefield epifluorescence to image cellular distribution of tagged proteins as well as total internal reflection (TIRF) imaging for surface expression of the proteins over time. These tools are useful for developing insights into the dynamic behavior of membrane channels and how their behavior affects disease states.