Ch 6 6.4 Membrane Potential 6.5 Cell Signaling

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

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

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

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

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+ = - 90 mV

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

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

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

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+

Processes influencing the RMP

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

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)

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?

How regulatory molecules affect their target cells

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.

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

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  _______________

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