Michael M. Tamkun, PhD
Primary teaching activities include organizing and lecturing in BMS 500 -- Mammalian Physiology, lecturing in various neuroscience courses, and organizing undergraduate seminar classes in biochemistry. This formal teaching involves excitable membrane molecular biology and physiology as it relates to nerve and muscle function. However, most of the teaching activity is centered in the research laboratory. Instruction here runs from the postdoctoral to the undergraduate level; for the Tamkun laboratory contains postdoctoral fellows, graduate students, and undergraduates pursuing independent research projects.
Research Interests -- Sodium Channels, Potassium Channels, Action Potentials, Cell Surface Localization
Ion channel regulation within neuronal and muscle membranes is an important determinant of electrical excitability in the nervous and cardiovascular systems, skeletal muscle, GI tract and uterus. Voltage-gated K[+] channels (Kv channels) play an important role in setting the resting potential and determining repolarization in these functionally diverse systems. Recent evidence suggests that Kv channels differentially target to specialized microdomains within the plane of most plasma membranes. These domains often concentrate a number of signal transduction molecules, making channel-specific trafficking significant from both a functional and localization standpoint.
Current projects in the lab include:
1. Analysis of ion channel trafficking using live cell, confocal laser scanning imaging. Here FRAP, FRET and photoactivatable GFPs will be or are being used to address the mechanisms by which different Kv channels move through distinct biosynthetic pathways. Adenovirus is used to infect cardiac myocytes and neurons in primary culture. This primary cell culture work will be best accomplished using knockout mice as the cell source since all necessary proteins but the channel under study are present.
2. Purification of Kv channels to identify components of the channel-containing macromolecular complex. Purification efforts thus far have most often employed antibody-based approaches. However, this approach is problematic since isoform-specific antibodies are most likely directed against regions involved in protein-protein interactions. For example, the available antibodies against Kv2.1 readily immuno-stain nerve cells but not cardiac myocytes or smooth muscle cells even though western analysis indicates the Kv2.1 channel is abundant in these cell types. Thus, we are tagging channels with new epitope tags, confirming proper trafficking, and then developing large scale purification techniques.
3. Create mice expressing tagged Kv channels under the control of the native promoter. Once the above efforts convince us we know how to tag a channel for trafficking analysis or purification without perturbing its synthesis, subcellular targeting or function, we will exchange one wild type allele coding sequence with that for a tagged "super channel." This will generate a mouse expressing normal levels of a channel appropriately tagged for both trafficking and purification studies. Importantly, the channel of interest can now be studied in any cell type in which it is normally expressed.
Deal KK, England SK, Tamkun MM. 1996. Molecular physiology of cardiac potassium channels. Physiol Rev 76:49-68.
Hulme JT, Coppock EA, Felipe A, Martens JR, Tamkun MM. 1999. O2 sensitivity of cloned voltage-gated potassium channels expressed in the pulmonary vasculature. Circ Res 85:489-497.
Martens JR, Navarro R, Coppock EA, Nishiyama A, Parshley L, Grobaski TD, Tamkun MM. 2000. Differential targeting of Shaker-like K+ channels to lipid rafts. J Biol Chem 275:7443-7446.
Martens JR, Sakamoto N, Grobaski TD, Tamkun MM. 2001. Isoform specific targeting of Kv channels to distinct lipid raft populations. Kv1.5 targets to caveolae. J Biol Chem 276:8409-8414.
O'Connell KMS, Martens JR, Tamkun MM. 2004. Localization of ion channels to lipid raft domains within the cardiovascular system. Trends Cardiovasc Med 14:37-42.
Martens JR, O'Connell KMS, Tamkun MM. 2004. Targeting of ion channels to membrane microdomains: Localization of Kv channels to lipid rafts. Trends Pharmacol Sci 25:16-21.