When GABA is applied to frog oocytes expressing GABA receptors, what is the resulting effect on membrane potential?

• A. Oocytes become hyperpolarized due to sodium entry
• B. Oocytes become depolarized and produce an action potential
• C. Oocytes become hyperpolarized due to chloride entry
• D. No change occurs in potential

Answer: (A)

The correct understanding of the effect of GABA on frog oocytes expressing GABA receptors is that oocytes become hyperpolarized due to chloride entry. When GABA, an inhibitory neurotransmitter, binds to its receptors, it opens channels that are typically permeable to chloride ions. In the case of many neurons, including those in amphibians, the intracellular concentration of chloride is lower than the extracellular concentration. Therefore, when GABA activates these receptors, chloride ions flow into the cell.

This influx of negatively charged chloride ions results in hyperpolarization of the membrane potential. Hyperpolarization means that the membrane potential becomes more negative compared to its resting state. This is consistent with the function of GABA as an inhibitory neurotransmitter, which serves to decrease the likelihood of action potentials in neurons.

So, the hyperpolarization that occurs due to the entry of chloride ions is key to understanding the physiological effects of GABA in this specific context, rather than any sodium entry or depolarization that could lead to action potentials.