CO2 Cellular function

Carbon dioxide is intrinsically linked to the ruminal epithelial function, playing a vital role in maintaining proper functioning of the rumen. The co-transport of CO2 and H2O through aquaporins, which are abundantly expressed in the ruminal epithelium, serves as the inherent fuel for nutrient uptake. Once inside the ruminal cells, water and CO2 undergo a transformation facilitated by the intracellular carbon anhydrase, converting them into bicarbonate and protons. These molecules then are exchange with various ruminal nutrients, including short-chain fatty acids and sodium. This intricate interplay of carbon dioxide, water, bicarbonate, and protons contributes to the efficient nutrient absorption and overall well-being of the rumen epithelium.

The cycle is complete once the secreted bicarbonate and protons, which play a crucial role in ruminal pH regulation, are efficiently reduced by the action of ruminal carbonic anhydrase into dCO2, or dissolved carbon dioxide. The efervescence of CO2 from the fluid liberates the H2O molecules, buffering the ruminal fluid.

In normal and in high dCO2 conditions the absorption of nutrients (SCFA- and Na+) is associated to the co-transport of ruminal water and CO2 via aquaporins. Intracellularly, water and CO2 are transformed by carbonic anhydrase (CA) which will provide protons (H3O+) and bicarbonate (HCO3-) to drive nutrient uptake. During CO2 holdup, dCO2 cannot escape the rumen liquid producing hyperosmolarity that will stop cellular H2O and CO2 absorption through aquaporins. The cells will increase the metabolism of SCFA- to produce the intracellular H2O and CO2 needed for transport, this will rise ketone bodies (secondary ketosis) and the intracellular depression of HCO3- triggers an inflammatory response normally seeing during SARA (Laporte-Uribe, 2023). Ruminal LPS and lactate are produced by bacteria as a reaction to the high dCO2 concentrations (Prescott and Stutts, 1955, Wright, 1960, Dehority, 1971).