Patch Clamp - PowerPoint PPT Presentation

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Patch Clamp

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1. A microscopic version of the end-plate current recorded with voltage clamp ... The pipette should be carefully fire-polished and clean ... – PowerPoint PPT presentation

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Title: Patch Clamp


1
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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?k ( Vm Ek )
  • Vm Ek50 mV ,?k 20 pS ? ik1 pA
  • Johnson noise current
  • snv(4kT?f/R)
  • ?f1 kHz , R1/20 pS , T293 K
  • k Boltzmanns constant ? sn0.018 pA
  • ? S/N56

5
  • R1 10 MO
  • Rchannel 51010 O
  • RT 10 MO
  • ? sn1.3 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
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