Membrane Potential

Question 1

• Electric force vs. osmotic force? Implications?
• Two forces acting on an ion? Creates what?
• Equilibrium potential is? Relates what? Each ion? If membrane potential = eq. potential? If they are not equal?
• Membrane potential?
• How to evaluate pump at steady state? (2) Same direction? Different direction? 2
• Number of excess ions in cell?

Answer 1

• Electric force much stronger; few ions needed to counter conc. differences
• Conc. gradient and electric potential difference; electrochemical gradient
• Voltage difference if a given ion was at equilibrium given ECF:ICF ratio; conc. gradient to electric force; has its own; ion is at electro-chem equilibrium; pump must exist
• Real difference in voltage between the ECF and ICF
• Look at [ ]i vs [ ]o to see which way it would move; look at ion charge vs. membrane potential; must be pump; compare eq. potential to mombrane potential to see if pumped or not
• Small compared to total number of ions

Question 2

• Bulk solutions?
• Does cell at eq. have to have same conc. in and out? Must follow what?
• Charge neutrality means what? Not what?
• Nernst Eq?
• If at steady state with no pumps?
• Na/K pump does what?
• Steady state def?
• Equilibrium def?

Answer 2

• Always neutral electrically
• No; Donnans rule = product of ion conc. in must equal product of ion conc. out
• # cations/anions the same in and out; inside equals outside
• E = -60 log ( [ ]o / [ ]i )
• -Vm = E
• 3 Na out; 2 K in costs 1 ATP
• Most cells; ion conc. aren’t chaning over time but energy maintains gradient
• Ion conc. don’t change over time and don’t cost energy

Question 3

• Driving force in cells?
• Membrane potentials sensitive to changes in? Not to changes in?
• Loss of NA to EC’s effect on Vm
• Sensitivity to K+ outside cell?
• Way to treat kyperkalemia?

Answer 3

• Difference b/n Vm and E
• [k+]o; [na+] o
• Very little
• Very; b/c starting conc. outside is so small
  C BIG K; calcium, bicarbonate, insulin, glucose, kayenolate