**Control of Cell Volume and
Membrane Potential**

**Slide 2**

**Basic problem**

**Basic solution**

**The cell at steady state**

**Typical ionic concentrations**

**Active pumping**

**Na**^{+}-K^{+}
ATPase

**Na**^{+}-K^{+}
ATPase

**Osmosis**

**The Nernst equation**

**Only very little ion
transfer**

**Electrical circuit model of
cell membrane**

**How to model I**_{ionic}

**Two common current models**

**Electrodiffusion: deriving
current models**

**The short-channel limit**

**The long-channel limit**

**Volume control: The
Pump-Leak Model**

**Charge and osmotic balance**

**Steady-state solution**

**RVD and RVI**

**RVD and RVI**

**Lots of interesting unsolved
problems**

**Ion transport**

**Steady state equations**

**Transport control**

**IMCD cells**

**Active modulation of the
membrane potential: electrically excitable cells**

**Hodgkin, Huxley, and
**

the Giant Squid Axon

**The **

reality

**Resting potential**

**Simplifications**

**Steady-state vs
instantaneous I-V curves**

**Example: Na**^{+} and
K^{+} channels

**K**^{+} channel gating

**Na**^{+} channel
gating

**Experimental data: K**^{+}
conductance

**Experimental data: Na**^{+}
conductance

**Hodgkin-Huxley equations**

**An action potential**

**The fast phase plane: I**

**The fast phase plane: II**

**The fast-slow phase plane**

**Oscillations**

**Where does it go from here?**