Electrochemical gradients Flashcards
how do transporters and channels have fundamentally different properties
a cells phospholipid bilayer limits the passage of charged molecules across the cell membrane (lipid part of the cell membrane has high electrical resistance)
gap junctions, membrane transporters and ion channels provide routes for charged molecules to cross the cell membrane
what do ion channel characteristics contain
selectivity
gating
how can channels be gated
mechanically
ligand and/or voltage-gated
what do all cells have
a membrane potential
what does Ohm’s law define
the relationship among membrane potential (voltage)
current
conductance (inverse of resistance)
I=CV
live cells resting membrane potential
Vm or RMP
is negative with respect to the extracellular fluid
electrically excitable cells resting membrane potential
neurons and myocytes
-30 to -70 mV RMP
they have a larger number of K+ channels open at rest
primary function of Na+/K+ ATPase
establishment of the concentration gradients for Na+ and K+
needed to generate resting, graded and action potentials
only mildly electrogenic
nt result of the actions of Na+/K+ ATPase is Vm of -5 to -12mV
ion reversal potential
also known as the equilibrium potential
membrane potential where the net flow through any open channel is 0
Erev the chemical and electrical forces are in balance
what equation do you use to calculate the Erev
the Nerst equation
R= gas constant
T= temperature in K
z= ion charge
F=Fraday’s constant
sodium ion equilibrium potential
+60mV
potassium ion equilibrium potential
-88mV
in order to calculate RMP what must you account for
the relative contribution of each channel type
expressed in terms of permeability P
resting membrane potential will be close in value to the reverse potential for the ion that carries the majority of the resting current
what can easily pass through the phospholipid bilayer
gases
some neurotransmitters
small amphiphilic compounds (most general anaesthetics)
what does the bilayer have high resistance to
the passage of current
3 types of membrane proteins that enable charged molecules to cross the membrane
gap junctions
electrical synapses
membrane transporters
what are gap junctions
large pores that form between 2 adjacent cells and can pass ions and small molecules
includes ATP
electrical synapses are a specialised form of gap junctions
what are membrane transporters
also known as pumps
integral membrane proteins that mediate facilitated diffusion or active transport of ions and other small molecules across the membrane
facilitated diffusion
occurs via specific transport proteins, permeases
only allow specific ions/molecules to pass through the membrane
three types of transporters
uniports
symports
antiports
uniports
move a single molecule
symports
move multiple molecules in the same direction
antiports
move multiple molecules in opposing directions
what do channels do
allow water or ions to flow rapidly through a water-filled pore
channels information
direct connection between the intracellular and extracellular spaces
move small molecules
always move charged molecules down their concentration gradients, passive process
dissipate concentration gradients
extremely high speed 10x10^6 molecules per second
pumps information
never any connection between the intracellular and extracellular spaces
can move larger molecules
using ATP, some pumps (anti ports) can move molecules against their concentration gradients, active
build up concentration gradients
slower 1 x 10^3 molecules per second
typical membrane potential
+40mV to -70mV
Vm
potential difference
relative measure
movement of one positive ion from the outside to the inside results in a +2 change in Vm
depolarisation
movement to a more positive membrane potential
hyperpolarisation
movement to a more negative membrane potential
principle intracellular cation
potassium
principle extracellular cation
sodium
principle anion
chloride
mainly extracellular
environment outside the cell compared to inside
inside is more negative than outside
more negative ions inside the cell
resting membrane potential as there is no active stimulus
how do you measure membrane potential
micro electrode
mammalian neuron at 37 degrees Nerst equation
K+ is -90
Na is +61
Cl- is -52
what is used to maintain the resting potential
sodium-potassium pump
action potential
generated in the presence of a stimulus
nerve endings are stimulated
sodium channels open
membrane is depolarised
membrane potential changes from -70 to +40
reaches the threshold potential
all sodium channels open
more sodium ions move into the cell
threshold/ all or nothing principle
when the membrane potential reaches +40mV the threshold is reached and all the sodium ion channels will open to allow influx of sodium ions into the cell
repolarisation
once the membrane is depolarised
sodium channels will close and the potassium channels will open
membrane is repolarised as the membrane potential becomes more negative
may fall into a temporary overshoot known as hyper polarisation
new action potential can’t be generated, known as the refractory period
sodium potassium pump maintains the potential
what occurs if there is an electrolyte imbalance
the equilibrium potential and membrane potential will change
hypokalaemia
more potassium ions leak out of the cell during the resting state
changes the membrane potential to a more negative value of -90
hyperkalaemia
fewer potassium ions move out of the cell through leaky potassium channels
resting potential becomes less negative
elevated plasma (extracellular fluid) K+ concentration
effect of current on membrane potential
direction of current alters the membrane potential
efflux of positive ions cell will become hyper polarised
influx of positive ions the cell may become depolarised and generate an action potential
what can cause a change in potassium ion concentrations
increased intake
decreased renal elimination
renal failure
adrenal disease
medications that alter kidney function
angiotensin-converting enzyme inhibitors
angiotensin II receptor blockers
potassium-sparing diuretics
non-steroidal anti-inflammatory drugs
increased release from intracellular stores due to tissue damage
effects of high potassium on the body
irregular heartbeat
changes in mood
chest pain
shortness of breath
weakening pulse
heart palpitations
kidney conditions
nausea, vomiting or diarrhoea
numbness or tingling
muscle weakness
most life threatening consequence of hyperkalemia
arrhythmia
cardiac arrest
due to depolarisation of the resting potential of cardia myocytes
