1. Chloride is a negatively charged ion (CI) that has a higher concentration out
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Question
1. Chloride is a negatively charged ion (CI) that has a higher concentration outside of the cell than inside of the cell. a.) Is the equilibrium potential negative or positive for chloride? Why? b.) Assume the concentration of Cl is 10 mM inside the cell and 100 mM outside the cell, and that there is an open chloride channel in the cell membrane. Will CI move into or out of the cell at a membrane potential of -40 mV? -65 mV? At which membrane potential will there be a higher net movement of Cl and why? 2. What concentration ratio of a divalent cation is created between the inside and outside of the cell if the resting membrane potential is -70 mV and the cell is only permeable to the divalent cation?Explanation / Answer
1.
a.) Equilibrium potential is the cell membrane potential at which net inflow/outflow of chloride ion is zero. So, To happen the equlibrium potential for chloride. This equlibrium/ reversal potential can be calculated from Nernst equation.
As chloride ions are negatively charge, if there is positive cell membrane potetial, there will chloride ion movement in either side of the cell membrane. So for chloride, equilibrium potential (cell membrane potentail) must be negative.
b) From nernst equation we know that equlibrium potential for chloride is -61 mV. For chloride concentration gradient is always into the cell.
At cell membrane potential -40mV : Chloride will move into cell(as the concentration gradient is toward inside cell) to make the inside more negatively charged and reach the equlibrium potential for chloride, which is -61mV
At membrane potential -65mV: Chloride ion will move out of cell to reduce the membrane potential to -61mV
At -40mV potetial there will more net chloride movement to compentsate (61-40)=21mV gap than (65-61)= 4mV voltage gradiant gap plus it is along the concentration gradient of chloride ion (from higher to lower).
2. Divalent cataion mean ion++: If we imagine each bivalent cataion have 2mV charge, to create a -70mV difference we need 36 divalent cataion( 72mV) outside of cell and 1 cataion (2mV) inside cell. So the concentration ratio (outside to inside is) = 36:1
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