Electrophysiology of the Cell Membrane Flashcards
What are the major inorganic ions that carry electrical currents (across membrane)
Ca 2+ , Na + , K + , Cl − , and HCO3-
What three integral membrane proteins are used for electric current flow
ion channels, electrogenic ion transporters and electrogenic ion pumps.
what things are involded in hormone secretion, ionic homeostasis, osmoregulation, and regulation of muscle contractility.
channels proteins
charge/lading is measured in?
coulombs
what is z for Cl-?
z=-1
what is e0?
unitary charge , 1.6022 × 10 −19
( ε r)=?
dielectric constant
( ℱ )=?
attractive electrostatic force
why cant Na move from water to inside of membrane?
(high ε) to the interior of a phospholipid membrane (low ε) ~36 kcal/mole. This value is 60-fold higher than molecular thermal energy at room temperature.
what is intracellular recording
The sharp tip of a microelectrode is gently inserted into the cell and measures the transmembrane potential with respect to the electrical potential of the extracellular solution, defined as ground (i.e., ψ o = 0).
What is the Vm of a skelatal muscle cell?
-90mV
what is E (E=Vm/a)
electrical field.
Skeletal muscle cells, cardiac cells, and neurons typically have resting membrane potentials of approximately .. to …mV; smooth-muscle cells have membrane potentials in the range of … mV; and the V m of the human erythrocyte is only about .. mV. However, certain bacteria and plant cells have transmembrane voltages as large as ….
Skeletal muscle cells, cardiac cells, and neurons typically have resting membrane potentials of approximately −60 to −90 mV; smooth-muscle cells have membrane potentials in the range of −55 mV; and the V m of the human erythrocyte is only about −9 mV. However, certain bacteria and plant cells have transmembrane voltages as large as −200 mV.
When are spectroscopic techniques used to meassure the Vm
very small cells such as erythrocytes, small intracellular organelles such as mitochondria, and fine processes such as the synaptic endings of neurons
how do spectroscopic techniques work
cells or membranes are labeled with an organic dye molecule and the absorption or fluorescence of the dye is monitored
what is another way of measuring Vm (not spectroscopic or microelectrode).
optically is to use cells that express genetically engineered voltage-sensing proteins that have been coupled to a modified version of the jellyfish green fluorescent protein (GFP).
what does the optical method for measuring Vm benefit from
it can see that Vm changes are similar but delayed in the more distant neural processes inaccessible to the microelectrode.
what 3 objects are needed for the fluorescent dye method?
light source
dichroic mirror
photodetector
(emmited red light changes with Vm
what ois resting potential
steady value (Vm) when the cell is not undergoing active responses
With what parameter does Vm have relationship?
Electrical field
what are electrogenic transporters
transporters that can generate a current that sets up and electric potential accros the membrane.
is the Na-K pump direct contribution to the Vm small or large?
small
What happens if you switch CL to SO4
you eliminate the contribution of anions to Vm
How is the Na-K pump responsible for Vm
indriect by generating and maintaining ion gradients
WHat is the planar lipid bilayer
artificial cell membrane
To what is the planar lipid bilayer similar intracellular recording or spectroscopic. and what is the main difference between PLB and the similar technieque
intracellular
both sides of the mebrane are accessible to manipulation
Why does one add a suffienct amount of a nonelectrolyte to the side with lower KCL concentration (Planar Lipid Bilayers)
to ellimante osmotic flow
What substance can you add to Planar Lipid Bilayer to eliminate osmotic flow.
mannitol
nonelectrolyte
is the planar bilayer permeable or impermeable?
impermeable
what are the minimal components for generating a Vm
impermeable membrane
unequal ion solutions (ion gradient)
ion-selective channels (conductance pathway)
what do ion channels do for the membrane
a conductance pathway lowering the resistance
what are diffusion potential
the membrane potential caused by , X diffuses down its concentration gradient (in planar-bilayer)
what is simmilar to the diffusion potential at equilibrium
equilibrium potential ( E X )
what gives the nernst equation
equilibrium potential ( E X )
What are the two ways to predict Vm without the discovery of ion channels
is to measure the movemnt of a single ion species through the membrane.
2. summing up the currents carried by each species of ions present
what is electrodiffusion?
process of ion permeation through the membrane
what is the constant vield assumption
the electric field (=the change in voltage with distance) is constant.
what is the Independence principle?
the movement of an ion through a membrane is independent from the movement of other ions
Px=Dx*β/ a.
what are the parameters
px= permeabilty coeffiecient
Dx is the diffusion coefficient in the mebrane
a= the thickness of the membrane
β is the membrane/water partition coefficient for the ion,
what does the electrodiffusion model assume
homogenous membrane
constant electric field
ions move independently from one another
a constant permeabilty coeffiecient.
what laws do we use do calculate current of a single ion (with electrodiffusion model assumptions)
- fick’s law of diffusion
- the movement of ions in an electric field ((electrophoresis)
- oHMS LAW
What is the goldman-hodgkin katz current equations a result of
- fick’s law of diffusion
- the movement of ions in an electric field ((electrophoresis)
- oHMS LAW
what is the Goldman-Hodgkin-Katz (GHK) current equation,
the constant-field assumption applied to Nernst-Planck electrodiffusion
what is Ix
the rate of ions moving through a membrane (ampere)
to what does the GHK equation relate the current of ion X?
internal external concentration of X, transmembrane voltage and the permability of the membrane to X
is the inward going current negative going current or positive going current
negative going current
in to the cell
is the outward going current negative going current or positive going current
positive going current
out of the cell
is inward flow of CL- inward or outward current?
outward, because current is always direction of positive charge.
what is the reversal potential equal to?
Nernst potential (Ex)
when Vm is more negative than Vrev what will cations do
move inward
when is the GHK voltage equation or the constant-field equation is valid
when zero net flux flowing across the membrane
when does VM equal Vrev?
at resting membrane potential.
What happens with hypoklamia to the TWIK-1 K2P channel
α becomes larger, causes depolarization that can trigger cardiac arrhythmia leading to cardiac arrest
what ion and cause has a high permeability to vertebate skeletal muscle cells
Cl, Cl − equilibrium potential in skeletal muscle is essentially equivalent to the resting potential
what is an EMF
voltage source of a battery.
electromotive force
what is the emf of an ion
the equilibrium potential
what is the variable resistor of K
the conductance provided by K channels
what is a capacitor
a device that is capable of storing charge
what is the capacitor of a cell
the lipid bilayer
what is capacitance
the magnitude of the carge stoped per unit potenial difference.
in farads
what is (ε 0 ), in capacitance
vacuum permittivity constant
what is (ε r ) in capacitance
the relative permittivity (dielectric constant) of the medium between the two plates
what is A in capacitiance formula
surface area (A) of one side of a plate
are cell membrane potential sustained by a small or large separation of charge
small
does Cl depolarize or hyperpolaryise
both in most cells depolarize
in skeletal cells hyper polarize
what is the capacitative current?
the current that only flows when Vm is changing.
how does a condensator (capacitor) produce current
when a voltage across a capacitor changes the capicator either loses or gains charge.
what is the time constant
The time required for the voltage to fall to 37% of its initial value
what is a square pulse
current or voltage is abruptly changed to a fixed value, held constant for a certain time, and returned to the original value.
what does square pulse of V do to Im
2 brief spikes
what does square pulse of I do to Vm
the voltage changes to a new value with a rounded time course determined by the RC value of the membrane.
what is electrophoresis
the movement of ions in an electric field
