Increased chloride conductance typically causes what change in neuronal excitability?

• A. Decreased excitability due to hyperpolarization
• B. Increased excitability
• C. No change
• D. Destabilization

Answer: (B)

Increasing chloride conductance makes the membrane more leaky to Cl−, pulling any membrane potential toward the chloride reversal potential. In most mature neurons, E_Cl is near or below the resting potential, so opening Cl− channels tends to hyperpolarize the cell or, at minimum, reduce the input resistance. This dampens the effect of excitatory inputs: EPSPs are smaller and less likely to reach threshold, making action potential firing less likely. In other words, higher Cl− conductance typically decreases excitability through inhibitory effects (hyperpolarization when E_Cl is sufficiently negative, or shunting inhibition when E_Cl is near the resting potential). There are exceptions in developing neurons where intracellular Cl− is high and E_Cl is depolarized, which can make Cl− conductance excitatory, but that’s not the common scenario.