Final answer:
Membrane potential influences the Gibbs free energy change (ΔG) for calcium ion import due to the electrochemical gradient. A more negative membrane potential increases the ΔG, requiring more energy for ion import against it. Membrane depolarization affects this process and may alter the required energy for Ca2+ movement.
Step-by-step explanation:
Effect of Membrane Potential on ΔG for Calcium Ion Import
Membrane potential, which is negative for most cells, impacts the Gibbs free energy change (ΔG) for the import of calcium ions (Ca2+) into the cell. The electrical gradient, established by a negatively charged interior, favors the movement of positively charged cations, such as Ca2+, into the cell. This movement is influenced by two forces: the chemical force (concentration gradient) and the electrical force (difference in charge across the membrane). Together, these create an electrochemical gradient.
In the context of membrane potential, a cell at rest typically has a voltage around -70 mV. As Ca2+ is imported into the cell, the membrane potential becomes less negative and may reach a depolarized state of approximately +30 mV for Na+ ions in the scenario of action potentials. This depolarization would require energy in the form of ATP to maintain ion gradients, affecting the ΔG for Ca2+ import.
The specifics of how membrane potential modifies ΔG depend on the magnitude of the potential and the concentration of ions on either side of the membrane. However, generally, a more negative membrane potential would increase ΔG, meaning more work is required to import Ca2+ against the electrochemical gradient, especially if it contrasts with the direction favored by the membrane's existing potential.