Patch Clamp

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• Patch Clamp

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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

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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

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

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• 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.

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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

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• Configurations of patch clamp

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• Single channel conductance

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• 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.

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