Week 5 Fitzakerley - Ion Channel Physiology Flashcards
What is Ohm’s Law?
V = IR
What substances are least likely to diffuse through a pure phospholipid bilayer?
Anything charged.
Na+, K+, Cl-
What three things provide routes for charged molecules to cross the cell membrane?
- Gap junctions
- Membrane transporters
- Ion channels
Why does the cell’s phospholipid bilayer limit the passage of charged molecules (especially ions) across the cell membrane?
The lipid part of the cell membrane has high electrical resistance.
What are four differences between ion channels and transporters?
- Ion channels:
- holes through membranes, BIDIRECTIONAL
- passage of small things (ions)
- always passive (with electrochemical gradient)
- high rates of transport
- Transporters:
- protein translocates (not open to both sides at once)
- passage of big things (glucose)
- passive & active
- slower rate of transport
Do ion channels or transporters set up concentration gradients?
Transporters set up concentration gradients.
Ion channels use concentration gradients.
Do ion channels or transporters have a larger impact on Voltage (V=IR)?
Ion channels.
Increased rate of flow (larger I)
V = I x R
What happens when red blood cells are placed in a hypotonic solution?
Water molecules enter the RBCs, causing them to lyse.
What happens when a cell with no aquaporins is put in a hypotonic solution?
Nothing changes.
(Cell with aquaporin allows water to rush in and eventually lyses.)
What are the two fundamental characteristics of ion channels?
-
Selectivity
- number/types of ions allowed through
-
Gating
- leak (always open)
- voltage
- ligand
- mechanically
In addition to ion channel gating, what mechanism can prevent the flow of ions through the channel?
Inactivation
What is the difference between closing and inactivating a channel?
- All gated channels can close, only some channels can inactivate
- Inactivation is random
Live cells have a resting membrane potential (RMP) that is negative with respect to what?
the Extracellular fluid
Why do electrically excitable cells such as neurons and myoctyes have a much larger negative RMP?
Because they have a larger number of K+ channels open at rest.
What things determine the extracellular ion concentrations?
Kidney
Diet
What things determine the intracellular ion concentration?
Transporters
(especially Na+/K+ ATPase)
What effect does the ELECTRICAL gradient have on ions?
Positive ions move toward negatively charged areas.
Positive ions move away from positively charged areas.
(Vm & Erev)
**Based on charge
***Electrical gradients will determine direction and magnitude of ion flow.
What effect does the CHEMICAL gradient have on ions?
Ions moved based on concentration gradient
High → Low
- Set up by transporters
- Used by ion channels
What is the equilibrium (reversal) potential?
The membrane potential where the net flow through any open channel is 0.
What two forces are in balance at Erev?
Chemical and Electrical forces
In order to determine the resting membrane potential (RMP), you must first determine what about each channel type?
Permiability (P)
The relative contribution of each channel type.
What value will the resting membrane potential (RMP) be close to?
The reversal potential (Erev) for the ion that carries the majority of the resting current.
Define depolarized in terms of the reversal potential.
More positive than the reveral potential.
Define hyperpolarized in terms of the reversal potential.
More negative than the reversal potential.
True or False: In neurons, the resting membrane potential is a constant negative value that is determined by the activity of the Na+/K+ ATPase.
False.
Homeostasis is dynamic, not constant.
ATPase sets up concentration gradients for ion channels to use.
*Ion channels determine resting membrane potential in neurons.
How do you re-establish the resting membrane potential, when extracellular K+is rising due to tissue damage?
Do not shock with defibrillator!
- Ca2+Gluconate
- regenerates ability to produce action potential
- Hyperpolarize cells by giving Insulin
- pumps K+ back into cells
- Dialyze
- reduce extracellular K+ concentration
What regulates the lysis of RBCs, and how does this change during Plasmodium vivax (Malaria) infection?
- Lysis of RBCs:
- change in osmolarity across the cell
- aquaporins allow water flow
- Lysis of RBCs in Malaria infection:
- malaria parasite eats hemoglobin to prevent a change in osmolarity initially as the parasite reproduces
- Hb is also a source of energy
- sequential activation of large anion transporter, K+ channels, Na+ channels
- malaria parasite eats hemoglobin to prevent a change in osmolarity initially as the parasite reproduces
What happens to the RBC in response to activation of the large anion transporter?
- Cl- flows out of the cell
- RMP of RBC = -15
- Erevof Cl- = -7.6
- Depolarization of cell until Vm ~ -7.6
- Small change, but cell still able to maintain homeostasis
What happens to the RBC in response to activation of large anion transporter AND K+ channels?
- K+ flows out of cell
- Erev of K+ = -85
- Cell hyperpolarizes to Vm ~ -85
- lose more Cl-
- cell contracts due to increasing change in osmolarity
What happens to the RBC in response to activation of large anion transporters AND K+channels AND Na+channels?
- Na+ flows into cell
- Erev of Na+= +83
- Cell depolarizes
- Cl- enters once Vm is greater than -7.6
- Too much for cell to handle
- Not able to maintain homeostasis
- CELL LYSIS!!!
What events happen before the Plasmodium vivax enters RBCs?
Bite → blood → liver (dormant 3-4 mths) →
*blood* → RBCs
*Replication of malaria and RBC lysis does not occur until the second time it enters the blood.
