Which molecule functions as a buffer for maintaining pH in RBCs?

Bicarbonate serves as a crucial buffer in maintaining the pH levels within red blood cells (RBCs). It operates through a well-established system known as the bicarbonate buffering system, which is essential for regulating the acid-base balance in the blood. When carbon dioxide is produced as a metabolic byproduct in tissues, it diffuses into the RBCs, where it reacts with water to form carbonic acid. This carbonic acid can then dissociate into bicarbonate and hydrogen ions.

The bicarbonate ions effectively neutralize excess hydrogen ions, helping to stabilize the pH within the red blood cells and, by extension, throughout the plasma. This buffering action is vital because even small changes in pH can have significant physiological consequences, affecting enzyme activity, oxygen transport, and overall cellular function.

In contrast, while carbon dioxide is involved in the process, it does not function as a buffer itself. Oxygen plays a critical role in respiration but has no role in maintaining pH. Nitric oxide, although important in various signaling processes within the vasculature, does not contribute to pH buffering functions in RBCs. Hence, bicarbonate is the molecule that specifically and effectively maintains pH balance in red blood cells.