1. Equipment for Intracellular Recordings

2. Extracellular Potential in a “Resting” Cell

3. Basis of Membrane Potentials: A Model Cell

4. Assume the membrane is permeable only to C +

5. The Gibbs-Donnan Equilibrium At 25 o C for univalent positive ions: Here the sign refers to direction of the gradient.

6. RMP Mind Problem #1 Draw vectors for: Δ G d for diffusion of the cation Electrical force acting on the cation Total force (the only one that matters) acting on the cation FOR THESE CONDITIONS: 1.Before cation permeability 2.A brief instant (dt) after permeability is established 3.Gibbs-Donnan equilibrium

7. RMP Mind Problem #2 What will be the sense of the charge on the inside of the cell if the anion is the only permeable ion? Explain.

8. Ionic Distributions in an Example Cell What is the sense of charge predicted by each ion? What is E m predicted by each ion at 25°C? Which ion(s) determine rmp? E M = - 98 mV E K+ = -101.4 mV E Cl- = - 97.5 mV E Na+ = + 64.7 mV Do the proteins matter?

9. Test of the Nernst Model