Which membrane transporter is considered electrogenic and translocates a net charge across the membrane?

• A. K+−Cl− cotransporter
• B. Na+−glucose cotransporter
• C. Ca2+−ATPase
• D. Na+−H+ exchanger

Answer: (B)

The Na+−glucose cotransporter is considered electrogenic because it moves sodium ions into the cell while promoting the inward transport of glucose, contributing to a net charge movement across the membrane. In this process, the flow of sodium ions down their concentration gradient not only brings glucose along but also adds a positive charge to the interior of the cell, creating a slight voltage difference.

In contrast, other transporters mentioned do not translocate net charge as effectively. The K+−Cl− cotransporter typically allows the movement of both potassium and chloride ions across the membrane without a net charge being displaced, as their movements often balance each other out. The Ca2+−ATPase primarily exports calcium ions out of the cell, which does carry a charge, but its primary function is to maintain calcium homeostasis rather than contribute to ongoing voltage differences across the membrane. The Na+−H+ exchanger, while it does move sodium ions into the cell and hydrogen ions out, also does not create a substantial net charge displacement that would classify it as electrogenic in the same manner.