Basic electrophysiology of electrically excitable cells

Question 1

dependency of Vm on extracellular [K]o

Answer 1

1. Vm is directly dependent upon the K transmembrane concentration gradient
2. dependency of Vm on K ion concentration is not significantly affected by the block of Na/K pump that sets up the ion gradient

even though transmembrane potential is very close to the equilibrium potential for potassium, it does deviate because the membrane is permeable to other ions

Question 2

Electrodiffusion and Ionic currents

Answer 2

electrodiffusion is defined as the movement of an ion down it electrochemical gradient thru transmembrane channel

Factors regulating transmembrane ionic current: electrochemical gradient, transmembran ionic permeability,

Question 3

true equilibrium potential

Answer 3

if membrane is permeable to only one ion, no energy is required to maintain the potential energy difference

Question 4

GHK equation

Answer 4

ionic permeability and concentration difference are the major factors that regulate the transmembrane current for each ion

Question 5

Cord conductance equation

Answer 5

Em=(gk/sum of g)Ek etc…

At rest Em is constant and thus in a steady state, and Em is 0 (if not Em is changing)

Question 6

Under steady State conditions

Answer 6

1. Na+ diffuses into the cell down the Electrochemicals gradient
2. Cl- diffuses into the cell
3. K diffuses out of the cell
4. intracellular NA and K concentrations are maintained via the NA/K ATPase and Cl is maintained by active Cl out of the cell

Question 7

Vm for electrically excitable cell for a cell membrane where Cl current is very low 0

Answer 7

Muscle cells have no Cl conductance:
Pcl is large and no active transport system for CL
Theres no net transmembrane current for Cl
Cl is in equilibrium so Ecl is equal to resting Vm

So Vm=-RT/f ln (Ki + alpha Nai)/((Ko + alpha Nao)

Alpha= permeability of na/k
as alpha goes up (ie NA permeability goes up, cell becomes more depolarized

small increases in extracellular K excite the cell