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Ion Conductance and Patch Clamp Methods

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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Ion Conductance and Patch Clamp Methods

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  1. Ion Conductance and Patch Clamp Methods February 3, 2012

  2. Housekeeping • Crawdad Care: • You are responsible for MONDAYONLY!

  3. 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?

  4. Patch Clamp Technique Single channel records

  5. 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?

  6. Factors that impact ionic current

  7. 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?

  8. 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

  9. 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

  10. Membrane potential impacts current [C]in = [C]out

  11. Ion concentration impacts current [C]in > [C]out [K+]in = 90 mM [K+]out = 3 mM

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