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Ion Conductance and Patch Clamp Methods. February 3, 2012. Housekeeping. Crawdad Care: You are responsible for MONDAY ONLY!. Review: Four laws Govern Ion Movement. Fick’s Law of Diffusion Ohm’s Law of Drift Einstein’s Relationship Between Diffusion and Drift Space-charge Neutrality

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Presentation Transcript
housekeeping
Housekeeping
  • Crawdad Care:
    • You are responsible for MONDAYONLY!
review four laws govern ion movement
Review: Four laws Govern Ion Movement
  • Fick’s Law of Diffusion
  • Ohm’s Law of Drift
  • Einstein’s Relationship Between Diffusion and Drift
  • Space-charge Neutrality
  • How do you measure ion movement in cells?
patch clamp technique
Patch Clamp Technique

Single channel records

what does patch clamp measure
What does patch clamp measure?
  • Current (pA)
    • What is current?
    • Ion flow (through a channel)
  • What does current depend on?
    • Kinetic behavior of the channel
    • Kinetic potential of ions across the membrane
      • Jdiff+ Jdrift or mz [C] (δV/δx) + D (δ[C]/δx)
    • What does the kinetic potential depend on?
factors that impact ionic current1
Factors that impact ionic current
  • Voltage
    • What is the relationship between current and voltage?
    • The current (I) through the channel is proportional to the voltage (V) applied:

I = g V

    • The value of the proportion is a constant (g),
    • This value is Channel Conductance
    • What does channel conductance depend on?
factors that impact channel conductance
Factors that impact channel conductance
  • Two!
  • The ease with which ions can flow through channels
    • “Channel Permeability”
  • The concentration of ions in the region of the channel
    • If ions are relatively scarce, an open channel can only pass a low current, no matter the permeability or the membrane potential
  • Open channel  permeability
  • Permeability + Ions  Conductance
what we ve seen so far
What we've seen so far
  • Patch clamp
    • reveals kinetics for individual channels
    • reveals ionic current through individual channels
  • What factors affect ion movement through channels?
    • Voltage difference across membrane (electrical potential)
    • Difference in concentration of ions across membrane
    • Jdrift + Jdiff
ion concentration impacts current
Ion concentration impacts current

[C]in > [C]out

[K+]in = 90 mM

[K+]out = 3 mM