Lecture 7 - Resting Membrane Potential Flashcards
What is meant by selective permeability?
Certain ions channels in a cells membrane are open at a particular time allowing movement of these ions into or out of the cell
What cells have a membrane potential?
All cells have a membrane potential
What is a membrane potential of a cell?
The electrical potential difference (difference in electrical charge) across the cells plasma membrane
What is membrane potential important for?
Cell to cell signalling
Providing IMMEDIATE energy source for ion transport (electrochemical gradient)
What is used to measure the membrane potential of a cell?
Microelectrode
Conducting solution
How is the membrane potential of a cell measured?
The fine glass pipette of one side of the microelectrode penetrates the cell membrane into the cell (without disrupting membrane structure)
Cell filled with conducting solution
Other part of the electrode remains extracellular and gets zeroed
Membrane potential then measured
What does the value of membrane potential actually mean? For example if membrane potential was measured as -90mV what does this actually mean?
The difference in charge of the inside of the cell compared to the outside
-90mV means that the inside of the cell is 90mV MORE NEGATIVELY charged than the outside of the cell
What is 1mV in Volts?
1mV = 0.001V
1mV = 10^-3 V
What is Resting Membrane Potential?
The electrical potential (charge) difference across the plasma membrane of the cell when the cell is not stimulated/excited
What does RMP stand for?
Resting Membrane Potential
What is the RMP of Cardiac ventricular myocytes and Atrial myocytes?
-85mV
What is the RMP of Neurones?
-70mV
What is the RMP of Skeletal muscle myocytes?
-90mV
What is the RMP of Smooth muscle myocytes?
-50mV
What is an excitable cell?
Cell that can fire action potentials
What is a non excitable cell?
Cell that can NOT fire action potentials
What is the normal range of resting membrane potentials for cells?
-10mV to - 100mV
Which cells in the body do not have a resting membrane potential?
Pacemaker cells (SAN cells)
Depolarise — Repolarise — Immediately depolarise — etc..
How does depolarisation occur in non excitable cells? (Vascular smooth muscle)
Graded potentials
Gradually changes
Occurs as a repsonse to stimuli
What happens to vascular smooth muscles as it gradually depolarises?
Muscle contraction
Vasoconstriction
What happens when hyperpolarisation happens in vascular smooth muscle cells?
Muscle relaxes and dilates
Vasodilation
What do ions require in order to cross the cell membrane?
Ion channels
What is the key feature of an ion channel that allows ions to flow through?
Aqueous hydrophilic pore
What are the 3 properties of channels?
Selectivity
Gating
Rapid ion flow (Always down ELECTROCHEMICAL GRADIENT)
What are the 3 main factors/ concepts that determine RMP of a cell?
Selective permeability to ions at rest
Relationship between electrochemical gradients and equilibrium potentials
Contribution of Na+/K+ ATPase
What is the main contributor (Ion channel) to resting membrane potential?
The leaky K+ channel
How does the leaky potassium ion channel play the main role in setting up resting membrane potential?
Membrane selectively permeable to K+ so K+ moves out of cell down Concentration gradient through leaky K+ channels
Anions cant follow out of the cell since the membrane is not selectively permeable to them
Internal environment more negative
Negative charge inside of cell eventually equally pulls on K+ trying to draw it back into cell with an equal force that the concentration gradient of K+ has on forcing K+ out of cell
No net movement of K+
Potassium equilibrium potential reached
What is meant by the equilibrium potential for an ion?
Its the potential difference for that ion at which the chemical gradient and electrical gradient are both equal and opposite
The draw from the electrical gradient into the cell matches the force of the ion moving out of the cell down its chemical concentration gradient
What is the net movement of K+ when the cell is at the Equilibirum potential for K+ (Ek)?
No overall net movement
What is the Nernst equation used to calculate?
The membrane potential at which an ion will be in equilibrium
What is the Intracellular concentration of Na+, K+, Cl- and Anion like compared to outside the cell?
Na+ = LOW in cell
K+ = HIGH in cell
Cl- = LOW in cell
Anions = HIGH in cell
Why are cells Resting Membrane potential not equal to the Equilibrium potential for potassium (Ek)?
Membrane not perfectly selectively permeable to K+. Other ions can leak across the membrane like Na+ and Ca2+. This makes the cell slightly more positive than Ek
What would the RMP of a cell that is PERFECTLY selectively permeable to Na+ if the E(Na) is +60mV?
+60mV
What affect does a cell becoming more selectively permeable to an ion have on the cells RMP?
Gets closer to the equilibrium potential for that cell
What conditions do unsynchronised action potentials (Delayed after depolarisations) cause to the heart?
Cardiac arrhythmias
What is the meaning of the equilibrium potential of an ion?
The concentration gradient of the ion movement of the cell is equal to the electronical pull of the ion back into the cell
What is the role of Na+/K+ ATPase in RMP?
Counteracts the inward flow of Na+ through leaky Na+ down the electrochemical gradient by pumping 3Na+ out for each cycle
Maintains the RMP
Using either “Major, Secondary or none” as a description, what is the contribution of these channel proteins on RMP?
Leaky K+ Channel
Leaky Na+ Channel
Transporters and exchangers
Na+/K+ ATPase
GLUT 1-4
Leaky K+ Channel: Major
Leaky Na+ Channel: Secondary
Transporters and exchangers: Secondary
Na+/K+ ATPase: Secondary
GLUT 1-4: None
