Final answer:
The change in membrane potential (Vm) when sodium ion permeability (P Na) is altered depends on the Goldman-Hodgkin-Katz voltage equation.
Step-by-step explanation:
The question seems to be about changes in membrane potential (Vm) when the permeability (P Na) of sodium (Na+) ions is altered. To understand how Vm changes with changes in P Na, we need to refer to the Goldman-Hodgkin-Katz (GHK) voltage equation. This equation considers the permeability of different ions to predict the membrane potential of a cell. Specifically:
Vm is the membrane potential,
P Na is the permeability to sodium ions,
P K and P Cl represent the potassium and chloride ions permeability respectively.
When P Na is changed, the relative contribution of sodium ions to the overall potential changes. If P Na is increased, sodium ions, which typically have a higher concentration outside the cell compared to inside, will contribute more to the charge difference across the membrane, potentially making the inside of the cell more positive (depolarizing the membrane).
On the other hand, if P Na is decreased to a value like 0.8, this means that there is a reduction in sodium ion permeability. This would generally cause the membrane potential to become more negative (hyperpolarization), since sodium ions are less able to enter the cell and contribute less to the membrane potential.
However, the exact change in membrane potential can only be accurately determined by using the GHK voltage equation and knowing the specific values for the permeabilities of all ions involved, along with their concentration gradients.