Membrane potential is influenced by ion conductances mainly through which mechanism?

• A. Opening of channels
• B. Diffusion due to concentration gradients
• C. Active transport by pumps
• D. Binding of ions to intracellular proteins

Answer: (A)

Membrane potential is set by how permeable the membrane is to different ions, and that permeability is controlled by opening and closing ion channels. When channels for a particular ion open, the membrane conductance for that ion increases, allowing ions to flow according to their electrochemical gradient and generating current. This current pulls the membrane potential toward that ion’s equilibrium potential, and the overall resting or active Vm is a weighted outcome based on the relative conductances of all ions involved. In short, gating of channels modulates conductance and thus shapes the membrane potential.

Diffusion along concentration gradients describes the driving force behind ion movement, not the mechanism that changes conductance. Active pumps maintain gradients over time but don’t acutely set the instantaneous membrane potential, and binding of ions to intracellular proteins doesn’t produce the currents that determine Vm.