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Department of Physiology and Biophysics

University of Colorado Department of Physiology and Biophysics
 

Alexander Polster, PhD

Postdoctoral Fellow in Kurt Beam's lab


Education:

PhD in Physiology 2011, Leibniz Universität Hannover, Germany: “FRET Reveals Substantial Reorientation of the Cytoplasmic Interface of the Skeletal Muscle DHPR in the Presence of RyR1”

Master of Science (MSc) 2005, Universität Osnabrück
Bachelor of Science (BSc) 2003, Universität Osnabrück


 

Positions:

since 02/2011: Postdoctoral Fellow at the University of Colorado, Denver;  Department of Physiology & Biophysics, Laboratory of Kurt G. Beam, PhD

2005-2006: Research associate at QIAGEN (Hilden, Germany), Laboratory of Dr. Christoph Ritt ‘Chemical and Biological research’


For the last eight years, I have been exploring the molecular mechanisms of coupling between the skeletal muscle L-type voltage-gated Ca2+ channel (1,4-dihydropyridine receptor, DHPR) in the transverse tubular (TT) membrane and the type 1 intracellular Ca2+  release channel (RyR1) of the sarcoplasmic reticulum (SR) in the laboratories of Drs. Kurt Beam & Symeon Papadopoulos. This interaction is the fundamental basis for excitation-contraction (EC) coupling in skeletal muscle.

To study the interactions of these proteins in a near-native environment, we use cultured muscle cells which are genetically null for DHPR subunits and/or RyR1. These muscle cells are injected with cDNA encoding native or altered calcium channels, followed by whole-cell patch clamp measurement of membrane currents, and photometric measurements of intracellular calcium. The work has shown that there is specialized, bi-directional signaling between the DHPR and RyR1 and identified regions of both the DHPR and RyR1 that are important for this signaling. However, these techniques do not establish whether the functionally important regions represent actual sites of physical contact between the DHPR and RyR1. For this reason, we have implemented approaches that could allow us to identify such interaction sites within intact muscle cells. One approach we currently use is to express cDNAs which encode calcium channels with fluorescent protein inserted at targeted sites, which permits the use of fluorescence resonance energy transfer (FRET), a technique that provides a sensitive measure of whether proteins are close (<10 nm) to one another. These experiments indicate that RyR1 may come into close apposition with two regions of the DHPR.

The long term goal of our work is to determine regions of close proximity between the proteins (i.e., potential sites of interaction) within the TT/SR junction and also to determine whether those regions undergo dynamic changes during physiological function. The sorts of approaches we are developing may be of general use for analyzing the molecular machinery underlying important functions in many cell types.

Recent Publications:
​2012 Polster, A., Ohrtman, J.D., Beam, K.G., Papadopoulos, S.
“Fluorescence Resonance Energy Transfer (FRET) Indicates that Association with the Type I Ryanodine Receptor (RyR1) Causes Reorientation of Multiple Cytoplasmic Domains of the Dihydropyridine Receptor (DHPR) α1S Subunit” J. Biol. Chem. 287: 41560-41568
​2011 ​Bannister, R.A., Polster, A.
„A shortcut to a skeletal muscle DHPR knock-in?” J Physiol 589 (19) 4645-4646
​2010 ​Mühlhausen A, Polster A, Theißen G, Mummenhoff K.
“Evolution of Fruit Dehiscence in Brassicaceae – Examples from Aethionema and Lepidium“ Hansen M (ed.). Proceedings of the Vth. International Symposium on Brassicas & XVIth. Crucifer Genetics Worshop, Lillehammer. Acta Horticulturae Vol 867, International Society for Horticultural Science, Leuven, pp. 207-219.
​2009 ​Mummenhoff, K., Polster, A., Mühlhausen, A., Theißen, G.
“Lepidium as a model system for studying the evolution of fruit development in Brassicaceae” J.  Exper. Bot. 60: 1503-1513; doi:10.1093/jxb/ern304
​2008 ​Ohrtman, J.D., Ritter, B., Polster, A., Beam, K.G., Papadopoulos, S.
“Sequence differences in the IQ motifs of CaV1.1 and CaV1.2 strongly impact calmodulin binding and calcium-dependent inactivation” J. Biol. Chem. 283, 29301-29311.
Conference Abstracts:
​2014 Polster, A., Linde, N.F., Beam, K.G., Papadopoulos, S.
“Expression of covalently linked DHPR CaV1.1 subunit multimers to investigate the teradic arrangement of DHPRs in skeletal muscle” Biophysical Journal

​2014 Polster, A., Linde, N.F., Filipova, D., Walter, A., Beam, K.G., Papadopoulos, S.
“Investigating the role of the tetradic arrangement of DHPRs in skeletal muscle excitation-contraction coupling” DPG Mainz, Germany

​2014 Polster, A., Tanabe, T., Moua, O., Beam, K.G.
“Multiple regions inhibit expression of CaV1.1 Ca2+ channels in non-muscle cells“ Biophysical Journal 106(2) pp. 136a

​2014 ​Bichraoui, H., Moua, O., Polster, A., Tanabe, T., Papadopoulos, S., Beam, K.G.
“Testing for direct interactions between the DHPR and the RyR1 cytoplasmic foot“
Biophysical Journal 106(2) pp. 135a - 136a

​2013 Polster, A., Bichraoui, H., Ohrtman, J.D., Beam, K.G., Papadopoulos, S
“The cytoplasmic foot of type 1 Ryanodine receptor targets junctionally, retrogradely enhances L-type Ca2+ currents and homo-tetramerizes” DPG Heidelberg, Germany

​2013 Polster, A., Ohrtman, J.D., Beam, K.G., Papadopoulos, S.
“The Cytoplasmic Foot of RyR1 Without the Membrane Spanning Domain Targets Junctionally and Retrogradely Enhances DHPR L-type Ca2+ Currents“ Biophysical Journal 104(2) pp. 445a

​2013 ​Bichraoui, H., Polster, A., Papadopoulos, S., Beam, K.G.
“The Cytoplasmic Foot of RyR1 Forms a Stable Homotetrameric Structure Despite Lacking the Membrane-Spanning C-terminal Domains“ Biophysical Journal 104(2) pp. 445a - 446a

​2013 ​Perni, S., Polster, A., Papadopoulos, S., Beam, K.G., Franzini-Armstrong, C.
“The Cytoplasmic Domain of the RyR1 Foot is Sufficient for DHPR (Cav1.1) Organization into Tetrads“ Biophysical Journal 104(2) pp. 446a

​2012 Polster, A., Linde, N.F., Walter, A., Ohrtman, J.D., Beam, K.G., Papadopoulos, S.
“Expression of concatemers of the DHPR 1S subunit to investigate the function of tetrads in skeletal muscle” ECCC Alpbach, Austria

​2012 Polster, A., Ohrtman, J.D., Beam, K.G., Papadopoulos, S.
“Correct Junctional Targeting and Retrograde Signalling to the Dihydropyridine Receptor (DHPR) by a Truncated Ryanodine Receptor (RyR1)” DPG Dresden, Germany

​2012 Polster, A., Ohrtman, J.D., Beam, K.G., Papadopoulos, S.
“FRET Reveals Substantial Reorientation of the Cytoplasmic Interface of the Skeletal Muscle DHPR in the Presence of RyR1” Biophysical Journal 102(3) pp. 362a

​2010 Polster, A., Papadopoulos, S.
“Association of the 1S I/II loop peptide with 1a results in translocation of the complex to the cell surface and in clustering” Biophysical Journal 98(3) pp. 714a
​2009 ​Ohrtman, J.D., Papadopoulos, S., Polster, A., Beam, K.G.,
 “Voltage- and calcium-dependent inactivation of 1C is suppressed in muscle cells and this suppression does not appear to be a consequence of insertion into triad junctions“, GRC Boston

​2008 Polster, A., Papadopoulos, S.
“Evidence for a close spatial arrangement of intracellular domains of the skeletal muscle DHPR using measurements of fluorescence resonance energy transfer (FRET) between CyPet and YPet in a non-destructive measuring variant”, Biophysical Journal 94(2) pp. 507a
​2007 ​Mummenhoff, K., Mühlhausen, A., Polster, A., Lobbes, D., Theißen, G.
“Comparative analysis of fruit dehiscence / indehiscence in Brassicaceae”, Plant Biology
​2005 Polster, A., Mummenhoff, K.
“The role of lignification patterns in dehescent and indehiscent fruits in Brassicaceae: A comparative anatomical approach“, XVII IBC Vienna