Lactate shuttle: Where do the hydrogen ions end up?

On the Aug 17th podcast, Trevor and Rob described how hydrogen ions (which are responsible for the acidosis incorrectly attributed to lactic acid in the past) co-transport out of the Type II muscle fibres with lactate, and that lactate actually needs a hydrogen ion to get through the transporter. Once through the MCT4s in the Type II fibres, do the hydrogen ions disassociate from the lactate, or are they required to accompany it through the MCT1s into the Type I fibres (which it seems would then just plunge the pH of those fibres)? If they hit the bloodstream, where do they ultimately go, as blood obviously needs to stay in a tight pH range itself? Is it as simple as a trip to the lungs where the hydrogen ions get expelled through exhalation?

The where do the H+ ions go is likely a complex answer, one place is the conversion of NAD to NADH. It most certainly is not through hydrogen gas. Also lactate by definition is the positive ion that is generated when lactic acid gives up its H+ ion thus becoming lactate. In other words it is what all acids do, donate a hydrogen ion.

Thanks, Scooter; I appreciate your input in helping me understand this process.

Hydrogen ions (protons) can get “consumed” by a variety of buffers, include carbonate and bicarbonate ions in the blood. Also, a lot of the protons that made the proton gradient across the mitochondrial membrane are coming from water. They leave the OH- inside the mitochondria when they get pumped out during oxidative phosphorylation, but they come back inside and “rejoin” their OH- counterpart when ATP is made through chemiosmosis.