Which procedure serves as the best negative control for studying endogenous GABA receptor function?

• A. Addition of GABA to wild-type oocytes
• B. Transfection of wild-type GABA receptor into insect oocytes
• C. Transfection of wild-type GABA receptor into Rdl-expressing oocytes
• D. Addition of GABA to mock-transfected frog oocytes

Answer: (D)

The choice of using mock-transfected frog oocytes as a negative control is appropriate because it provides a baseline measurement for any observed effects of GABA on receptor function without the influence of the GABA receptors themselves. This approach allows researchers to ascertain whether the addition of GABA produces a response that is specifically due to the presence of GABA receptors being studied. By utilizing mock-transfected oocytes, which do not express the relevant receptors, any response can be attributed solely to the experimental conditions rather than receptor activity, thereby ensuring that any observed effects from GABA in other experimental setups are indeed due to the actions of the GABA receptors rather than non-specific effects or background noise.

In contrast, the other options either involve the presence of GABA receptors or do not serve as adequate controls. For instance, adding GABA to wild-type oocytes or transfecting wild-type receptors does not establish a control since these circumstances inherently include the receptors that the experiment seeks to elucidate. In the case of transfecting wild-type receptors into Rdl-expressing oocytes, the effect of the GABA receptors is being directly tested rather than controlled for, making it unsuitable as a negative control as well.