Final answer:
Decrease in sodium conductance in a cell will result in the membrane potential becoming more negative due to less depolarization caused by the inward flow of sodium ions.
Step-by-step explanation:
If the sodium conductance decreases in a cell with a membrane potential of -75mV, the membrane potential will become more negative. This can be explained by understanding the role of sodium in creating the membrane potential. Sodium ions (Na+) are more concentrated outside the cell than inside, and they carry a positive charge. Under normal conditions, when sodium channels are open, Na+ flows into the cell along its concentration gradient, which reduces the negative charge inside the cell, a process known as depolarization.
The resting state of the membrane is around -70mV, which is maintained by the selective permeability of the membrane and the action of the sodium-potassium pump. Since sodium ions are positive, their inward flow makes the interior of the cell less negative. If the conductance or permeability to sodium decreases, meaning less Na+ enters the cell, there will be less depolarization, and the inside of the cell will remain more negative, thus increasing the membrane potential in the negative direction.