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34 Cards in this Set

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  • Back
Why do we care about electrophysiology?
Because ALL local and propagated electrical signals generated by a cell are driven by changes in the resting Em.
Why is electrophysiology essential?
It is necessary for maintaining cell, tissue, and organism homeostasis.
The ability of an ion to travel through a semipermeable membrane
What 2 factors regulate the magnitude w/ which each permeable ion contributes to the resting membrane diffusion potential?
1. Transmembrane concentration difference of ea permeable ion
2. Mobility of permeable ion WITHIN the membrane relative to ions of opposite charge.
What is MOBILITY of an ion?
The velocity of ion movement
Unit of Driving Force
What does difference in cation vs anion mobility have to do with Membrane Potential?
Leads to a:
-SEPARATION of charge
-Attractive force betwn ions
What are the 2 determinants of ion intramembrane MOBILITY?
1. Diameter/shape of each ion and the pore thru which it goes
2. Ionic/Vanderwaals forces btwn ions and AA's in proteins facing the inner channel pore
An equal pos and neg charge separated by a finite difference
What is Diffusion Potential a result of?
Dipoles crossing the membrane in a nonrandom order due to force of a chemical gradient.
Is the dffusion potential caused by a difference in charge between two components?
NO - the intra/extracellular compartments are electroneutral actually; the separation of charge is ONLY IN THE MEMBRANE.
What is the 'state' nature of the Diffusion Potential?
STEADY STATE - requires a constant input of energy to maintain the chemical gradient.
What is the equation for simple diffusion potential?
Pcat-Pan 2.3RT [IP]o
Ediff = -------- x ----- x ----
Pcat+Pan nF [IP]i
Units of Ediff
millivolts mV
What is the permeability of each ion proportional to?
Its intramembrane diffusion coefficient (D)
What is the Diffusion Coefficient (D) proportional to?
The intramembrane mobility of an ion (beta)
What else is permeability of an ion proportional to?
the number of open channels in the membrane for each particular ion.
What does 2.3RT/nF = ?
60 mV (at 37 ' C)
When is the Nernst potential equation used instead of the simple diffusion potential equation?
When one of the members of a cation/anion pair is IMPERMEABLE to the membrane.
How is the nernst equationd different from that for simple diffusion potential?
It is only for one ion (the cation), and so permeability is not a factor.
What does the diffusion potential become when one member of a cation/ion pair is impermeable?
Becomes the equilibrium potential for the permeable ion.
What is an Equilibrium Potential?
The condition where a CHEMICAL driving force is BALANCED by an EQUAL/OPPOSITE ELECTRICAL force.
What is the equilibrium potential for potassium in a mammalian nerve or muscle fiber?
-89 mV
What is the normal K concentration inside/outside a mammalian nerve/muscle cell?
Inside = 140 mM
Outside = 4.7 mM
What happens to individual chemical/electrical potential differences when equilibrium potential is reached?
Is energy required to maintain the equilibrium potential for an ion?
How much change in intracellular K would have to occur to set up an Ek of -88 mV (instead of -89 mV)?
For a squid axon membrane:
0.00001% - too small to detect.
What is the normal concentration of Ca2+ inside/outside a mammalian nerve or muscle fiber?
Ca inside = 10^-7 M
Ca outside = 1.6 x 10^-3 M
Based on the concentration gradient where does Ca want to go?
INTO the cell - there is much more outside than inside.
How neg/pos would a cell have to be to balance the concentration gradient and prevent Ca influx?
VERY positive (to prevent the positive charge from rushing in)
What would the Eca be if the membrane were to become permeable to it?
126.7 mV
What equation is used for calculating the total resting membrane potential?
GHK - goldman hodgkin katz
What ions are included in the GHK equation for a squid axon?
Na, K, Cl
For a squid axon the measured resting Em is:
-65 mV
What is the effect of extracellular K on the resting Em in a squid axon?
Increasing K outside will make the cell Em be closer to the Ek (hyperpolarize).