1. به نام خدا

2. Patch Clamp

3. Opposing views on the time course of the single-channel current
1. A microscopic version of the end-plate current recorded with voltage clamp
2. All-or-none manner

4. Problem in the measurement of single-channel currents
ik=Υk ( Vm – Ek )
Vm – Ek=50 mV ,Υk =20 pS → ik=1 pA
Johnson noise current
σn=√(4kTΔf/R)
Δf=1 kHz , R=1/20 pS , T=293 K
k= Boltzmann’s constant → σn=0.018 pA
→ S/N=56

5. R1= 10 MΩ
Rchannel= 5*10^10 Ω
RT= 10 MΩ
→ σn=1.3 pA

6. The micropipette tip is around 1 µm diameter so measurement is unaffected by spatial variations and is hence “space clamped”, the “clamp” in the name “patch clamp” arises from this feature.

7. Considerations to ensure adequate signal to noise ratio
A high resistance seal
The pipette should be carefully fire-polished and clean
Cells should be clean and free of connective tissue
Application of gentle suction

8. Configurations of patch clamp

9. Single channel conductance

10. The choice of tip diameter of around 1 µm is about ten times larger than available intracellular micropipettes. This results in a lower tip resistance, a desirable factor to achieve a lower noise, as noted above. On the other hand, it may mean that more than one channel may find itself under the patch electrode; an examination of the recorded signal will reveal whether, in fact, only a single channel is accessed.

11. با تشکر