Biomedical & Biophysics Research at TcSUH : Electromagnetic Properties of Biological Systems

1. Biomedical & Biophysics Research at TcSUH:Electromagnetic Properties of Biological Systems John H. Miller, Jr. Department of Physics and Texas Center for Superconductivity University of Houston Summer 2005 Houston Quarknet Workshop June 24, 2005

2. Fundamental Principlesof biological systems • Emergence: Higher organizing principles emerge independently of the details of the microscopic Hamiltonian. (Anderson, Laughlin, Pines). • Information; Bioinformatics: Biological systems carry, preserve, and replicate information. Information is encoded via genetic code, sugar code, histone code, splicing code, gene regulation code ... • Convergent increase in complexity: The information content in an organism is vastly greater than that of its genome. • Natural Selection; Evolution: Similar principles may extend to non-biological systems (eg. language, music, culture). In biology, evolution is partly driven by mutations. TcSUH

3. Fundamental Principles(continued) • Metabolism; Bioenergetics: Living systems consume free energy: U – TS. The total energy is conserved (Uin = Uout) so Sin << Sout. Organisms consume ‘negative entropy’: - S = k log (1/Nstates). (Schrödinger “What is Life”.) • Quantum Protectorate: Quantum mechanics plays a crucial role in preserving information. Discrete gaps between energy levels enable stability of molecules (DNA, proteins, etc.). Lifetime of a molecule can be long: t ~ texp[D/kT], so at T ~ 300 K, if D ~ 1.8 eV, then t ~ 30,000 years. • Biological systems are complex, dynamically evolving materials. Condensed matter physics phenomena include: diamagnetism, charge density waves, dielectric response, ferroelectricity, piezoelectricity, quantum tunneling, excitons, and proposed biological superconductivity. TcSUH

4. Electromagnetic Interactionsare vital to living systems. • Electromagnetism is dominant in chemical and biological processes. • Biological macromolecules (in water) are highly charged &/or have strong electric dipole moments. • Both repulsion and attraction (eg. in presence of Ca2+) can occur between like charged polyelectrolytes. • Electromagnetic interactions can be extended to long distances by charge density waves, microtubules, etc. • Live cells exhibit electromotility, especially outer hair cells. TcSUH

5. Effects of an external electric field • At low frequencies, most of the potential drop is across the plasma membrane. • Induced potential: Um(w,q) = 1.5 E0R cosq [1 + iwtm]. • 5 V/cm field  Um ~ 15mV for a 20mm radius cell. TcSUH

6. Oscillatory field affects membrane proteins. • AC fields can actually drive cation transport in membrane pumps, even in the absence of ATP (Tsong, Astumian, et al). • Oscillatory fields also induce conformational changes. • Resulting motion of electric dipoles and charges generates harmonics. TcSUH

7. P-type ATPases TcSUH

8. Nonlinear response: Measurement of induced harmonics • A sinusoidal electric field is applied to the cell suspension. • At low frequencies (< 1 kHz) we use a SQUID to probe the currents. • A spectrum of harmonics, induced by membrane pumps, is recorded. (Nawarathna et al, APL 2004) TcSUH

9. Probing membrane pumps in yeast cells 3 V/cm 23 Hz TcSUH

10. Harmonic response of yeast after adding glucose 45 Hz 3 V/cm TcSUH

11. Asymmetric Junction Model • AC voltage drives conformational changes & cation transport. • Threshold voltages, V1 & V2, and time scales, t1 & t2. TcSUH

12. ATP Synthase Can probe internal organelles at kHz freqs. TcSUH

13. Budding yeast cells (S. cerevisiae) uncoupled mitochondria Probing the mitochondrial electron transport chain Nonlinear harmonic response Peaks are suppressed by adding potassium cyanide. TcSUH

14. Analogy to Coulomb blockade and time-correlated single-electron tunneling. Section of a tunnel junction array from a CBT sensor. The bright spots are tunnel junctions. Electron Transfer via Quantum Tunneling Pathway for ET from cytochrome c to active site of CcO For a recent review see: A. A. Stuchebrukhov, “Long-distance electron tunneling in proteins,” Theoretical Chem. Accounts, 110, 291 (2003). Discovery of activationless ET: DeVault & Chance (1966) Theory of ET reactions: Rudolph Marcus (Nobel Prize in Chem. 1992) Pilet et al. (2004) PNAS 101, 16198 Protein environment of the heme rings a and a3. The dominant ET pathway from heme a to a3 is shown as a dotted line. (Tan et al., BPJ 86, 1813 (2004)) Iron atom in heme a = e- queing point: feeds 4 e-s into an O2 molecule held at the Cu – Fe active site at heme a3. 4e- + 4H+ + O2 2H2O TcSUH

15. Nonlinear harmonic response in presence of light Probing the electron transport chain in chloroplasts TcSUH

16. Absorption spectra of various chlorophylls Frigaard et al. (1996), FEMS Microbiol. Ecol. 20: 69-77 Theory: Frenkel excitons in cylindrical aggregates Reaction center & light harvesting complexes of photosystem 2. (Top view) M. P. Bednarz, “Dynamics of Frenkel excitons in J-aggregates,” Ph.D. Thesis, Groningen, 2003. Photosynthetic electron transport chain TcSUH

17. Charge Density Waves (A) Uncondensed and (B) condensed F-actin, mediated by charge-density wave of divalent cations. T. E. Angelini, et al. PNAS 100, 8634 (2003). Charge density waves also proposed to form in membranes. TcSUH

18. Microtubules Anisotropic diamagnetism reported for microtubules. MTs also proposed to be ferroelectric. a-b tubulin dimer MT cytoskeleton Very large dipole moment! ~ 1500 debye = 5 x 10-27 C m. A microtubule may act as a ferroelectric with a “melting” temp. of ~57ºC. Brown & Tuszynski, Phys. Rev. E56, 5834 (1997). TcSUH

19. Microtubules: Electrostatic Interactions MTs radiating from centrosome Analogy: Electrostatic repulsion of hair. MT growth: 1. During mitosis Nanoscale electrostatics may play a key role in prometaphase, metaphase, and anaphase-A. Intracellular pH peaks during mitosis. L. J. Gagliardi, J. Electrostatics54, 219 (2002). 2. After depolymerization (Moscow State University) Artificial mitotic spindle, R. Heald, et al. (1996) Nature 382, 420-425. TcSUH

20. Live cells & proteins show dielectric responses that decrease with frequency. TcSUH

21. Tubulin dimer suspensions show strong dielectric response. Free tubulin dimers become “frozen out” as they polymerize (self-assemble) to form microtubules when T > 0º C.  Reduced concentration of free dimers. TcSUH

22. Tubulin dimer suspensions: conductivity vs. frequency. TcSUH

23. Prestin:A Membrane Protein Involved in OHC Electromotility Has 12 transmembrane domains; may form a tetramer; high density (~1/(20nm2)) in membrane. • Mediates OHC length changes to tune hearing frequencies • • has homology with sulfate transporters • operates at microsecond rates up to 100kHz • • voltage-to-force converter • – Electromotility • – Cochlear amplifier • – Incomplete anion transporter Zheng et al, Nature405, 149 (2000). P. Dallos & B. Fakler, 2002 TcSUH

24. Linear dielectric response: Prestin-transfected yeast vs. control. We see slight differences between S. cerevisiae expressing prestin vs. control samples. Miller et al., J. Biological Physics 2005. D =ep(f)/ep(f=f0)- ec(f)/ec(f0). Frequency range appears consistent w/ OHC piezoelectric resonances. Rabbitt et al. 2004. TcSUH

25. Other CMP Phenomena: Diamagnetism High Field Magnet Lab – University of Nijmegen Partly due to disipationless screening currents in aromatic rings. Anisotropic diamagnetism in microtubules, actin, fibrin…. Lowest energy p orbital of an aromatic ring, constructed from a superposition of pz-orbitals. The p-electron moves freely in a torus following the conjugation path of the molecule. TcSUH

26. Dr. George Zouridakis prepares a patient for MSI epilepsy source localization study at Hermann Hospital, Houston, Texas. Examples of medial temporal sources of activity evoked during a word-recognition task. Biomedical Applications: Biomagnetism • Magnetic fields produced by action potentials: • Magnetoencephalography (MEG), MCG, MGG, MMG, MRG, etc. TcSUH

27. Impedance Magnetocardiography (I-MCG) • ECG measures the electrical potentials generated by bioelectric currents in the heart. • MCG measures the weak magnetic fields due to bioelectric currents resulting from the propagating action potentials in the heart (eg. A. Brazdeikis) • I-MCG measures changes in impedance during the cardiac cycle due, in part, to changes in blood volume. Can probe cardiac ejection fraction and other properties. TcSUH

28. I-MCG Setup Noise measurements inside and outside the shield TcSUH

29. I-MCG recording using High-Tc SQUID TcSUH

30. Simulated current density during the cardiac cycle Atrial Systole Diastole(I) Ventricular Systole Diastole(II) TcSUH

31. Magnetic Resonance Imaging (MRI) TcSUH

32. MRI: Twin-Horseshoe HTS 2-T Receiver Probe (84.4 MHz, J. Wosik) Patterned on a double sided 2” YBCO film on LaAlO3 The probe inside a plastic liquid nitrogen cryostat TcSUH

33. MRI: 2-Tesla MR Image of Rat spinal-cord 4 dB gain brain TcSUH

34. Conclusions • Physics concepts can contribute to understanding of biological processes and lead to biomedical applications. • Experimental tools of condensed matter physics and materials science can play an important role in characterizing biological systems. TcSUH

35. Acknowledgements • University of Houston • Jarek Wosik (MRI), Audrius Brazdeikis (MCG), D. Nawarathna, Hugo Sanabria, Vijay Vajrala, James Claycomb, Gustavo Cardenas, David Warmflash, Jarek Wosik, William Widger, Jeffrey Gardner • Baylor College of Medicine • William Brownell, Fred Pereira • Funding • TcSUH, Welch Foundation, • NASA-ISSO TcSUH