1. Ch 6 6.4 Membrane Potential 6.5 Cell Signaling

2. SLOs Describe the equilibrium potential for Na+ and K+
Describe the membrane potential and explain how it is produced
Distinguish between synaptic, endocrine, and paracrine regulation
Identify where receptor proteins are located based on the type of ligand molecule

3. Resting Membrane Potential
IC and EC compartments are in electrical disequilibrium. Reasons:
_____________________________
__________ unequal Na+ and K + distribution
Membrane most permeable to _____
K+ is major _____cellular cation
Na+ is major _____cellular cation 10

4. Electro-Chemical Gradients accross plasma membrane
One more time:
Electro-Chemical Gradients accross plasma membrane
ECF
ICF
Made possible by cell membrane
Created via
Active transport
Selective membrane permeability to certain ions and molecules
Membrane potential (difference) = unequal distribution of charges across cell membrane
Measured in mV

5. Separation of Electrical Charges
If membrane was permeable to only one type of ion  value of membrane potential would be equal to the equilibrium potential for that ion.
Equilibrium potential = value when electrical force exactly opposes concentration force so that there is no net change in the number of ions on each side of the membrane.
Physiol. Measurements are always on relative scale ! 3

6. Effects of K+ Alone on Membrane Potential: K+ Equilibrium Potential
Steady state or dynamic equilibrium
EK+= Membrane potential difference at which K+ movement down concentration gradient equals movement down electrical gradient
In other words: At EK+: electrical gradient is equal to and opposite concentration gradient
EK+ = mV

7. Effects of Na+ Alone on Membrane Potential: Na+ Equilibrium Potential
Steady state or dynamic equilibrium ENa+= Membrane potential difference at which Na+ movement down concentration gradient equals movement down electrical gradient In other words: At ENa+: electrical gradient is equal to and opposite concentration gradient ENa+ = + 66 mV

8. Resting Membrane Potential (RMP)
Membrane Potential: Difference between electrical charge inside and outside of cell (ECF by convention 0 mV
Membrane Potential  separation of charges creates potential energy
Resting : The potential of a cell at rest. Cell not producing any impulses  all cells have it
Measuring Membrane Potential

9. Resting Membrane Potential Mostly Due to Potassium
Cell membrane
impermeable or almost impermeable to Na+, Cl - & Pr –
permeable to K+
 K+ moves down concentration gradient (from __________ to ____________ of cell)
 Excess of neg. charges inside cell
 Electrical gradient created
Neg. charges inside cell attract K+ back into cell

10. However, other ions do contribute to RMP.....
Small amount of Na+ leaks into cell Na+/K+-ATPase plays role in RMP by pumping out 3 Na+ for 2 K+ pumped into cell In most cells the resting potential is between -65 and -85 mV (average in neuron  -70 mV)
Resting cells permeable to K+ and Na+

11. Processes influencing
the RMP

12. Key Point Review of RMP
Steady state not an equilibrium. Passive and active forces counterbalance one another to achieve steady state
K+ and Na+ leak through “leak” channels
Membrane is more leaky to ___+ than ___+
Na/K pump returns ions
ECF and ICF are neutral; unpaired ions are lined along the membrane
Changes in the RMP is how cells produce electrical signals

13. Cell Signaling Cells communicate using chemical signals Types:
Paracrine signal - cells signal nearby cells
Synaptic signal - neurons release neurotransmitters
Endocrine signal - endocrine cells release hormones into the blood stream
(Gap junctions)

14. Receptor Proteins Chemical messengers bind to specific receptors
200 different cell types in human body are estimated to have  30,000 different receptor types
Where are receptors located?
What determines receptor location?

15. How regulatory molecules affect their target cells

16. Second Messengers are used for Signal Transduction
Signal molecule (ligand) binds to receptor.
Intermediaries, called second messengers, are sent inside the cell to affect change
Cyclic adenosine monophosphate (cyclic AMP or cAMP) is a common second messenger. Also Ca++ etc.
cAMP activates other enzymes.
Cell activities change in response.

18. G-Proteins Most Signal Transduction uses G-Proteins
G-proteins are made up of 3 subunits – alpha, beta, and gamma
One subunit dissociates when a signal molecule binds to the receptor and travels to the enzyme or ion channel

19. Most Signal Transduction uses G-Proteins
100s of G protein-coupled receptor types known
G protein is membrane transducer (activated via GTP binding  name!)
Activated G proteins
open ion channels, or
alter intracellular enzyme activity, e.g.: via cAMP (2nd messenger)  activates PK enzyme  _______________

20. The end Clinical Investigation:
Jessica, a physiology student who takes a diuretic drug.....
Explain what...
...happens if cell becomes more permeable to K+
...maximum resting membrane potential a cell can have
The end