Biomedical & Biophysics Research at TcSUH : Electromagnetic Properties of Biological Systems John H. Miller, Jr. Department of Physics and Texas Center.

Biomedical & Biophysics Research at TcSUHBiomedical & Biophysics Research at TcSUH::Electromagnetic Properties of Biological SystemsElectromagnetic 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

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Fundamental PrinciplesFundamental Principles of biological systemsof 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.

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Fundamental PrinciplesFundamental Principles (continued)(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 ~ exp[/kT], so at T ~ 300 K, if ~ 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.

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Electromagnetic InteractionsElectromagnetic Interactions are vital to living systems.are 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.

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Effects of an external electric fieldEffects of an external electric field

At low frequencies, most of the potential drop is across the plasma membrane.

Induced potential: Um(,) = 1.5 E0R cos [1 + im].

5 V/cm field Um ~ 15mV for a 20mm radius cell.

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Oscillatory field affects membrane proteins.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.

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P-type ATPasesP-type ATPases

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Nonlinear responseNonlinear response: : Measurement of induced harmonicsMeasurement of induced harmonics

0-5 V1-100 kHz

cell suspension

1 cm

1.5

cm

sample cell(top view)

Au pins

SR 780 analyzerSQUID controller

magnetic shield

SQUID

sample cell(side view)

N2(l)dewar

0-5 V1-100 kHz

cell suspension

1 cm

1.5

cm

sample cell(top view)

Au pins

1 cm

1.5

cm

sample cell(top view)

Au pins

SR 780 analyzerSQUID controller

magnetic shield

SQUID

sample cell(side view)

N2(l)dewar

SR 780 analyzerSQUID controller

magnetic shield

SQUID

sample cell(side view)

N2(l)dewar

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)

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Probing membrane pumps in yeast cellsProbing membrane pumps in yeast cellsVariation of the third harmonic vs

Frequency

0

50

100

150

200

250

0 10 20 30 40 50 60 70 80 90 100 110

Frequency Hz

Th

ird

ha

rmo

nic

a

.u

.8mM [VANADATE]

Yeast

Variation of the harmonic vs Applied electrical field

-100

0

100

200

300

400

500

600

0 1 2 3 4 5 6

Electrical fie ld V/cm

Th

ird

ha

rmo

nic

a

.u

.8mM [VANADATE]

Cells

3 V/cm

23 Hz

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Harmonic response of yeast after adding glucoseHarmonic response of yeast after adding glucose

45 Hz

3 V/cm

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Asymmetric Junction ModelAsymmetric Junction ModelAC voltage drives conformational changes & cation transport.

Threshold voltages, V1 & V2, and time scales, 1 & 2.

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Can probe internal organelles at kHz freqs.Can probe internal organelles at kHz freqs.

ATP Synthase

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Probing the mitochondrial electron transport chainProbing the mitochondrial electron transport chain

Nonlinear harmonic response

I

signal output(single f requency )

test f ixture R1

display

data out

SR780 s ignal analy zerampl if ier c ircu it

biol

ogi

calc

ells

Ch1

I

signal output(single f requency )

test f ixture R1

display

data out

SR780 s ignal analy zerampl if ier c ircu it

biol

ogi

calc

ells

Ch1

Budding yeast cells (S. cerevisiae)

Peaks are suppressed by adding potassium cyanide.

uncoupled mitochondria

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Electron Transfer via Quantum TunnelingElectron Transfer via Quantum Tunneling

Pilet et al. (2004) PNAS 101, 16198

Pathway for ET from cytochrome c to active site of CcO

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

Section of a tunnel junction array from a CBT sensor. The bright spots are tunnel junctions.

Analogy to Coulomb blockade and time-correlated single-

electron tunneling.

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)

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Probing the electron transport chain in chloroplastsProbing the electron transport chain in chloroplasts

Variation of the second harmonic vs frequency for cloroplasts

-2

0

2

4

6

8

10

12

0 3 6 9 12 15 18 21 24 27

Frequency kHz

Sec

on

d H

arm

oin

c m

V

With out light

with light

I

signal output(single f requency )

test f ixture R1

display

data out

SR780 s ignal analy zerampl if ier c ircuit

biol

ogi

calc

ells

Ch1

I

signal output(single f requency )

test f ixture R1

display

data out

SR780 s ignal analy zerampl if ier c ircuit

biol

ogi

calc

ells

Ch1

Nonlinear harmonic response in presence of light

-5

0

5

10

15

20

25

30

0 3 6 9 12 15 18 21 24 27

Frequency kHz

Sec

on

d H

arm

on

ic m

V

With light

Light+K3FeCN2

-5

0

5

10

15

20

25

30

0 3 6 9 12 15 18 21 24 27

Frequency kHz

Sec

on

d H

arm

on

ic m

V

With Light

Light+K3FeCN2

Light+K3FeCN2+NH4Cl

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Photosynthetic electron transport chainPhotosynthetic electron transport chain

Reaction center & light harvesting complexes of photosystem 2. (Top view)

Absorption spectra of various chlorophylls

Frigaard et al. (1996), FEMS Microbiol. Ecol. 20: 69-77

Theory: Frenkel excitons in cylindrical aggregates

M. P. Bednarz, “Dynamics of Frenkel excitons in J-aggregates,” Ph.D. Thesis, Groningen, 2003.

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Charge Density WavesCharge 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.

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MicrotubulesMicrotubulesAnisotropic diamagnetism reported for microtubules.

MTs also proposed to be ferroelectric.

tubulin dimer

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. E 56, 5834 (1997).

MT cytoskeleton

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MicrotubulesMicrotubules: : Electrostatic InteractionsElectrostatic Interactions

MT growth:

1. During mitosis

2. After depolymerization

(Moscow State University)

MTs radiating from centrosome

Analogy: Electrostatic repulsion of hair.

Nanoscale electrostatics may play a key role in prometaphase, metaphase, and anaphase-A.

Intracellular pH peaks during mitosis.

L. J. Gagliardi, J. Electrostatics 54, 219 (2002).Artificial mitotic spindle,

R. Heald, et al. (1996) Nature 382, 420-425.

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Live cells & proteins show dielectric responsesLive cells & proteins show dielectric responsesthat decrease with frequency.that decrease with frequency.

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Tubulin dimer suspensions show strong dielectric response.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.

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

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PrestinPrestin::A Membrane Protein Involved in OHC ElectromotilityA Membrane Protein Involved in OHC Electromotility

Zheng et al, Nature 405, 149 (2000). P. Dallos & B. Fakler, 2002

Has 12 transmembrane domains; may form a tetramer; high density (~1/(20nm2)) in membrane.

• has homology with sulfate transporters• operates at microsecond rates up to 100 kHz• voltage-to-force converter – Electromotility – Cochlear amplifier – Incomplete anion transporter

• Mediates OHC length changesMediates OHC length changes to tune hearing frequenciesto tune hearing frequencies

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Linear dielectric response: Linear dielectric response: Prestin-transfected yeast vs. control.Prestin-transfected yeast vs. control.

We see slight differences between S. cerevisiae expressing prestin vs. control samples.

Miller et al., J. Biological Physics 2005. = p(f)/p(f=f0) - c(f)/c(f0).

1010

102

103

104

105

Frequency (Hz)

Control Yeast

εr

102 103 104 105

Prestin Yeast

10

102

103

104

105

εr

10

Frequency (Hz)

102 103 104 105

Frequency range appears consistent w/ OHC piezoelectric resonances.Rabbitt et al. 2004.

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Other CMP Phenomena: Other CMP Phenomena: DiamagnetismDiamagnetism

High Field Magnet Lab – University of Nijmegen

Partly due to disipationless screening currents in aromatic rings.

Lowest energy orbital of an aromatic ring, constructed from a superposition of pz-orbitals.

The -electron moves freely in a torus following the conjugation path of the molecule.

Anisotropic diamagnetism in microtubules, actin, fibrin….

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Biomedical ApplicationsBiomedical Applications: Biomagnetism: Biomagnetism Magnetic fields produced by action potentials:

• Magnetoencephalography (MEG), MCG, MGG, MMG, MRG, etc.

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.

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Impedance Magnetocardiography (I-MCG)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.

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I-MCG SetupI-MCG Setup

1 10 1000.1

1

10

100

1000

field

no

ise

(nT

/Hz1/

2)

frequency (Hz)

Noise measurements inside Noise measurements inside and outside the shieldand outside the shield

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1 2 3 4 5

-1.0

-0.5

0.0

0.5

1.0

EC

G

and

I-

MC

G (

a.u.

)

time (seconds)

I-MCG recording using High-I-MCG recording using High-TTcc SQUID SQUID

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0.0830.2370.3910.5440.6980.8521.0051.1591.3131.4661.620

j ( A/m2 )Current Density

0.0830.2370.3910.5440.6980.8521.0051.1591.3131.4661.620

j ( A/m2 )Current Density

Simulated current density during the cardiac cycleSimulated current density during the cardiac cycle

Diastole(I) Atrial Systole

Ventricular Systole Diastole(II)

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Magnetic Resonance Imaging (Magnetic Resonance Imaging (MRIMRI))

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MRIMRI: Twin-Horseshoe HTS 2-T Receiver Probe : Twin-Horseshoe HTS 2-T Receiver Probe (84.4 MHz, J. Wosik)(84.4 MHz, J. Wosik)

Patterned on a double sided 2” YBCO film on LaAlO3

The probe inside a plastic liquid nitrogen cryostat

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MRIMRI: 2-Tesla MR Image of Rat: 2-Tesla MR Image of Rat

4 dB gain

spinal-cord

brain

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• 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.

ConclusionsConclusions

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AcknowledgementsAcknowledgements

• 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