Electrical SynapsesElectrical Synapses

Or Shemesh

March 2010

shemesh72369@gmail.com

• Relatively non-specific.• Molecular movement through passive diffusion.• Selectivity based upon molecular size (- allow movement of molecules whose molecular weight <1000Da.) (- allow movement of molecules whose diameter < 1.2nm.)

Cell #1Cell #1 Cell #2Cell #2

Gap junctionsGap junctions

Structural arrangement of Gap junctionsStructural arrangement of Gap junctions

ConnexinConnexon

( A hemi-channel)

Structural arrangement of Gap junctionsStructural arrangement of Gap junctions

Two docked connexons(a gap junction channel)Gap junction plaque

Electric synapses Electric synapses vs.vs. Chemical synapses Chemical synapses

Synaptic Synaptic delaydelay

No delay0.2ms-2ms

Direction of Direction of conductanceconductance

Bi- directional, but not necessarily symmetric

unidirectional

Two coupled cells in VitroTwo coupled cells in Vitro

Cell 2

Cell 1

II22II11

The equivalent electrical circuitThe equivalent electrical circuit

r1

rc

r2

Cell 2Cell 1

V1V1 V2V2

The equivalent electrical circuitThe equivalent electrical circuit

V1V1

I2I2I1I1V2V2

The equivalent electrical circuitThe equivalent electrical circuit

r1

rc

r2

Cell 2Cell 1

V1V1 V2V2

Basic conceptsBasic concepts

I1, I2

V11,V22, V21, V12

V 1 1

Voltage in cell Current injected to cell

r1

rc

r2

Cell 2Cell 1

V1V1 V2V2

Input resistancesInput resistances

21

21

1

1111

)(

rrr

rrr

I

VR

c

c

r1

rc

r2

Cell 2Cell 1

Input resistancesInput resistances

21

12

2

2222

)(

rrr

rrr

I

VR

c

c

If rc << r2 and rc << r1

Then 21

212211 rr

rrRR

r1

rc

r2

Cell 2Cell 1

Transfer resistancesTransfer resistances

1

2121 I

VR

2

1212 I

VR

r1

rc

r2

Cell 2Cell 1

r1

rc

r2

Cell 2Cell 1

21

121221 rrr

rrRR

c

Cell 2Cell 1 Cell 2Cell 1

Coupling coefficientsCoupling coefficients

Potential in un-injected cell

Potential in injected cell

rrV

VCCc

2

11

2112

1

1

rrV

VCCc

1

22

1221

1

1

A typical traceA typical trace

I1

V11 V12

V21 V22

I2

Cell 2Cell 1Traces!Traces!

0 0.5 1.0 1.5 2.0

-0.5 nA, injected to cell 2 (left cell).

Cell1Cell1

Cell2Cell2

Cell 2Cell 1

-0.5 nA, injected to cell 1 (right cell).

Traces!Traces!

Cell1Cell1

Cell2Cell2

Cell 2Cell 1

Cell1Cell1

Cell2Cell2

Traces!Traces!

+0.4 nA, injected to cell 2 (left cell).

Cell 2Cell 1

accommodation

summation

Traces!Traces!

+0.4 nA, injected to cell 2 (left cell).

Cell1Cell1

Cell2Cell2