Ion Conductance and Patch Clamp Methods: Part 2

1. February 6, 2012 Ion Conductance and Patch Clamp Methods: Part 2

2. Snacks! Advice! Tips! Encouragement! Answers! 2/24 MCAT Q&A:  When to take it?  Should I take a prep class?  Does anyone really look at the writing component?  How do I deal with test anxiety? How many times can I/should I take it? 3/2 When is it the right time to apply?  Should I apply this year just to get some experience?  Does it matter what month I apply? When do I know when I'm ready? 3/9 Letters of Rec:  Packets? Committee Letters?  Interfolio? Whom should I ask?  How can I help my letter writers write the strongest letter they can? 3/30 AMCAS: Submitting the best application.  What experiences should I list?  When can I start?  Is there a fee-assistance program? 4/13 What schools should I apply to?  How many schools?  Private or Public? D.O. vs. M.D.?  Can/should I apply to both? 4/20 Personal Statement:  What are the do's and don'ts?  What resources do we have on campus to help?  How many drafts?  How do you start? 4/27Secondaries & Interviewing:  What's on them?  When do I need to get them in?  How can I tailor my application to each school?  What's the interview like? What resources do we have to practice the interview? 5/4 Drop in Q&A: Any other questions? Want to discuss particular elements of your application? Need some encouragement? The UST Health Professions Committee presentsApplying to Medical School a free Friday afternoon workshop series Fridays 3-4 pm OWS 251 To register, email jrprichard@stthomas.edu

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

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

5. Can a potential (electrical) force exactly offset the concentration force? • From before, -mz [C] (δV/δx) + D (δ[C]/δx) • Written slightly differently, using molar concentrations and derivatives (I can show you): (I don’t think so) V2-V1 = RT/zF (ln[C] 2/[C] 1) where: V2 – V1 is the membrane voltage ( Vm) R is the thermodynamic gas constant T is the temperature (°K) z is the valence of the ion F is the Faraday constant [C]2 /[C]1 is the ratio of ion concentrations across the membrane

6. Can a potential (electrical) force exactly offset the concentration force? • Vm = RT/zF (ln[C]2/[C]1) At room temperature, RT/zF is pretty close to 25 mV, and multiplying by 2.31 gives us the (base 10) log: Vm= 58 log [C]out/[C]in The Nernst Equation Gives Vmwhere electrical potential difference between inside and outside of the cell exactly offsets the concentration gradient for a particular ion This Vm The Equilibrium Potential

7. The Equilibrium Potential • If the concentration force (Jdiff) and the electrostatic gradient (Jdrift) for a particular ion are at equal strength opposing in direction, the ion is said to be at equilibrium • The membrane voltage (difference in electrical potential between the inside and outside of the neurons) at this point is the Equilibrium Potential for that ion • Ions may still cross the membrane, but there will be no current (no net flow of ions)

8. Example: Movement of K+ Ions Concentration Force Compartment 2 Compartment 1 Electrical Force K+ Cl- Cl- K+ K+ Cl- K+ Cl- Cl- K+ K+ Selectively permeable to Potassium (K+) Cl- Cl- Cl- Cl- K+ K+ K+ K+ K+ Cl- Cl- Cl- K+ K+ Cl- Cl- K+ Cl- K+ Equilibrium

9. Ionic Pressures in the Neuron

10. Structure of ion channels