Adventurous Motility - Rice Universitybioewhit/courses/bioe592/mat/Brownell/Synapse2003 lecture.pdf=± =±κεε κεε Assume: Physiological medium 0.14 M External and internal surface

Synaptic Transmission in Hair CellsW.E. Brownell

[email protected]

Sensory Neuroengineering, Rice8 October 2003

Hypothesis:OHC electromotility evolved from

hair cell synaptic mechanisms.

Edge of a Myxococcus xanthus colony - individual bacteria showing adventurous gliding motility, time lapse 600x speed (Kaiser lab website - Stanford).

Adventurous Motility

Outer membrane ripples on motile cells: Coincidence or functional roles?

OHC -Dieler et al. 1991

Oscillatoria -Adams et al. 1999

Flexibacter BH3 -Dickson et al. 1980

Trilaminate Walls

Oscillatoria –Adams et al. 1999

OHC

Neural membrane curvature Mechano-Electrical Transduction

Neurotransmission

Hair Cells Have Two Functions

Hair Cell Neurotransmission

Hudspeth, 1983Compton’s Interactive Encyclopedia, 1997

The output is neural

Frequencyincrease

The organ of Corti SensitiveSynapse

• Continuous release of neurotransmitter

• Rate of release modulated by < mV changes in membrane potential

Patterns - hair cells & photoreceptors

connectingcilium

kinocilium

Light dependent transmitter release

Dark – more release Light – less release

Schaeffer & Raveola, 1978

Phototransduction - dark current

The dark current depolarizes the membrane potential resulting in maximal neurotransmitter release. Light blocks the depolarizing current and decreases neurotransmitter release.

Visualizing the silent current

Geisler, 1974

Inner hair cell afferent synapse

Siegel & Brownell - 1986

Ribbon synapses

Lenzi & von Gersdorff, 2001

Ampullary organ of the North American Catfish

Mullinger, 1964

3-D reconstruction of frog hair cell synaptic ribbon

Lenzi et al. 1999

Recording from the synapse

Glowatzki & Fuchs, 2002

Interval between neurotransmitterrelease is Poisson

Glowatzki & Fuchs, 2002

Temporal precision

Kiang et al., 1965

Phase locking

Brownell, 1975

Intensity - invariance

Anderson, 1971

Specialized CNS synapses

Rowland et al., 2000

Preserve temporal coding

Protein-Protein Interactions in the Active Zone Matrix

Martin, 2002

Proteins bring membranes together

Weber et al., 1998

Vesicle fusion

Torri-Tarelli et al., 1985

Membrane fusion

Markin & Albanesi, 2002

(A) Parameters of the stalk.(B) Hemifusion,

- initial stage.(C) Hemifusion,

- transmonolayers contact.(D) Complete fusion

- fusion pore.

The fusion pore

attached to cellular membrane

Farrell & Cox, 2002

Geometry

xy

z

0 30-30-10

10

0

x (nm)

z (n

m)

0 30-30-10

10

0

x (nm)

cytosol cytosol

vesicle

extracellular

xy

z xy

z

0 30-30-10

10

0

x (nm)

z (n

m)

0 30-30-10

10

0

x (nm)

cytosol cytosol

vesicle

extracellular

Model

Ener

gy

Pore Reaction Coordinate

formation

fluctuation

expansion

50 k

T

Where do we get the energyto bend the membranes?

Phospholipids:the forgotten molecules

Don’t forget water

Membrane self assembly

Marrink, Lindahl, Edholm & Mark, 2001

+25 ns

Surface tension

attr

actio

n←

Ener

gy →

repu

lsio

n

Intermolecular distance

warmer

cooler

(

µ,

∂γ=−∂G

)TA

the energy required to increase the surface area of a liquid by a unit amount

Electrical potential changes γ:Lippmann mercury voltmeter

G. Lippmann, Ann. Phys. 149 (1873) DC Grahame (1947)

Voltage dependent membrane tension

Petrov & Sachs, 2002

Includes a differential change in surface tension at the two membrane interfaces

HEK electromotilitymeasured under voltage clamp with AFM

Zhang et al., 2001Mosbacher et al., 1998

V(+)

Voltage dependent membrane motion

Zhang et al., 2001

Voltage dependentpressure changes in squid axon

Terakawa, 1984

Electrical potential changes γ:Lippmann mercury voltmeter

G. Lippmann, Ann. Phys. 149 (1873) DC Grahame (1947)

Lippmann equation

Gabriel LippmannNobel Prize, physics 1908

A Gibbs adsorption equation for a polarizable interface,

∂γ=− ∂ −Γ∂µ−σ ∂oAS T E

:

o

-2 )

-2surface charge (Cm )-1: surface tension (Nm )

: electrical potential difference (V): chemical potential (V): temperature ( K ):surface concentration one component (moles m

:int erfacial entr

σ

γ

µ

Γ

o

A

E

T

S 2-1opy per unit area (JK m )−

contains the observed relation between surface charge and the ratio of the change in surface tension to the change in electrical potential,

( , )

ο

µ

∂γσ −∂

=TE

( , )

ο

µ

∂γσ −∂

=TE

Integrate the Lippmann under these boundary conditions:

εε κo=Ci

2j j2

j o

n z

RT

εε

= ∑2κ F1.

2.

p

dd oi i i i

ddm mi i i i

when

o e e e e

e e e ep

when and when

and

(V ) (V )

- q ) (V ) + q ) (V )

γ =γ γ =γ

γ =γ γ =γ

οο

οο

σ σ σ σ

σ σ σ σ

m

At voltage

Upon polarization to voltage V

= - = -

= -( = -(

oV

Voltage Dependent Tension

: j j

o w

Faraday's constant; n : concentration of species, j; z valency of species, j; R: gas constant;: permittivity of free space; : dielectric constant of water; : capacitance of double layer

ε ε

F

C

22 22

1 1

o om e m e ei i iV

e ie oo i

(C )T B B ( V ) C B B V

B B

≈ + ∆ + − σ + σ ∆

=± =±κ εε κ εε

Assume:Physiological medium 0.14 M External and internal surface charge -0.025 and -0.015 C/m2

Charging occurs by ions adsorbing onto or desorbing from∆V = 100 mV

Energy ≅ Pore Area * TV1000-5000 nm2 * 46µN/m10-50 kT

Tension is a linear function of voltage under physiological conditions (∆V< 100 mV)

: ; mvoltage dependent tension C membrane capacitance:VT

Flexoelectricity:coupling of membrane curvature of with the electric field

characterized in biological membranesby Petrov

Todorov, 1993

The flexoelectric effect

pillar

Plasma membrane

Spectrin

∆c

Vm1 Vm2

+≈

L

D

W

Cb

fffcUεεε0

D Cb

o w L

c membrane curvature; f flexoelectric coefficient (dipole); f flexoelectric coefficient (charge);: permittivity of free space; : dielectric constant of water; :dielectric constant of m: : :

ε ε ε embrane

Liquid Crystal Nature of BiomembranesProtein and lipid molecules comprising biomembranes

possess dipole moments

Dipoles contribute to the flexoelectric effect• curvature deformation changes membrane polarization

EP

PE

As c is increased, dipoles become more aligned increasing the polarization of the membrane

Direct flexoelectric effect

pore fluidcytosol

fused mem

brane

Ps Ps

-0.005 -0.001-0.003

4

3

5

2

Uf(

x 10

3 , µV

) 1

0Cb(nm-1)

Uf

pore fluidcytosol

fused mem

brane

Ps PsPs Ps

-0.005 -0.001-0.003

4

3

5

2

Uf(

x 10

3 , µV

) 1

0Cb(nm-1)

-0.005 -0.001-0.003

4

3

5

2

Uf(

x 10

3 , µV

) 1

0-0.005 -0.001-0.003

4

3

5

2

Uf(

x 10

3 , µV

) 1

0Cb(nm-1)

Uf

+≈

L

D

W

Cb

fffcUεεε0

The synaptic amplifier

Intrinsic tuning: - electrical

- membrane cycling

OHC electromotility – the other membrane based motor

Baylor:Amy Davidson, Ph.D.Brenda Farrell, Ph.D.

Olivier Lichtarge, M.D., Ph.D.Fred Pierera, Ph.D.Peter Saggau, Ph.D.

Buffalo:Fred Sachs, Ph.D.

Ken SnyderJohns Hopkins:

Aleksander S. Popel, Ph.D. Alexander A. Spector, Ph.D.

Rice:Bahman Anvari, Ph.D.

Robert M. Raphael, Ph.D.URLs: http://www.bcm.tmc.edu/oto/research/cochlea/

http://www.bioflexoelectricity.org

Collaborators

Hofmeister effect

Clarke & Lüpfert, 1999ClO4 > SCN > I > NO3 > Br > Cl > F > SO4

anion adsorption at membrane interface

Oliver et al., 2001I > Br > NO3 > Cl > HCO3 > F > SO4

Tension affectsvesicle recycling

Dai et al., 1997

Hyperpolarization & depolarization affect the charge on each interface

cytoplasmicextracellularmembrane

V

x=∞ x=-∞x=0 x=-δ

ψt

RestHyperpolarization Depolarization

V = ψ(-∞) - ψ(∞)= ψ(- ∞)

ψt = ψ(-δ)- ψ(0)Ψt : potential difference across the membrane V : transmembrane potential difference

V

ψt

x=0 x=-δ

V

ψt

x=0 x=-δ