Final answer:
The electrical driving force would push Na⁺, K⁺, and Ca²⁺ ions into the cell due to the negative membrane potential attracting these cations, while Cl⁻ and HCO₃⁻ ions would be pushed out since they are anions and the internal negative charge repels them.
Step-by-step explanation:
To determine the direction of the electrical driving force for each ion when the cell membrane potential is negative, we must consider the charge of the ion and the existing membrane potential. A negative cell membrane potential favors the influx of positively charged ions (cations) and the efflux of negatively charged ions (anions).
- Na⁺ (sodium) inside: The electrical force would drive Na⁺ ions into the cell because they are cations and the inside of the cell is negatively charged.
- K⁺ (potassium) inside: Although K⁺ ions are positively charged, the high internal concentration may drive them out. However, the negative membrane potential encourages K⁺ ions to enter the cell.
- Cl⁻ (chloride) outside: The electrical driving force would direct Cl⁻ ions to move out of the cell due to the negative internal charge repelling anions.
- HCO₃⁻ (bicarbonate) outside: Similarly, the electrical driving force would push HCO₃⁻ ions out of the cell because they are anions.
- Ca²⁺ (calcium) inside: The electrical driving force would encourage Ca²⁺ ions to enter the cell as they are cations and there's a negative potential inside the cell.
The electrical driving force acts in conjunction with a chemical force (concentration gradient) to create an electrochemical gradient, which regulates ion movements across membranes.