Beta Alanine Suffocates Cardiomyocytes, Taurine Lets Them Breath Again: Taurine Regulates Mitochondrial Protein Synthesis and Protects Mitochondria Against Superoxide Generation.

Image 1: Beta alanine and taurine;
the former interferes with uptake
and reactions that involve the latter.
Having listened to the last installment of the Amino Acids for Super Humans series you are already familiar with the antagonism of the two beta-amino acids ("beta-" indicates that those are not part of the 22 proteinogenic amino acids) beta alanine and taurine. Being structurally very similar, both share a single transporter, so that high levels of beta alanine decrease/inhibit taurine uptake.

Like a partial agonist, beta alanine also interferes with the actions of taurine by inhibiting reactions that involve the former, so that the cardiomyocytes Jong and his colleagues from the Universities of South Alabama, USA, and Kobe, Japan, incubated with 5mM beta alanine for 48h induced a 45% decrease in taurine content in the neonatal rat cardiomyocytes. The sudden lack of taurine "enhanced superoxide generation, the inactivation of the oxidant sensitive enzyme, aconitase, and the oxidation of glutathione" (Jong. 2011), or, put simply, induced mitochondrial oxidative stress.
Associated with the increase in oxidative stress was a decline in electron transport activity, with the activities of respiratory  chain complexes I and III declining  50–65% and oxygen consumption falling 30%.
The decline in the activity of ND5 and ND6 respiratory chain complex subunits produced a "bottleneck" effect. Its almost as if you were trying to breath through a mask with two automated, taurine-powered openings. If you run out of "fuel", the valves in the openings won't open completely, you will gasping for air and (I bet) will become severely stressed.
Figure 1: Oxygen consumption [in % of baseline] in control and in cardiomyocytes incubated with 5mM beta alanine.
(data adapted from Jong. 2011)
Before you do now flush all your beta alanine and beta alanine containing products down the toilette, consider this: The existing data on the safety of beta alanine makes it quite clear that taken in individual (even large doses) your body is well able to avoid that the supplemental beta alanine "floods" your heart muscles, depletes their taurine stores and suffocates their mitochondria. How so? Well, firstly it can distribute the beta alanine over millions of brain and muscle cells (something that obviously could not happen in the petri-dish with isolated cardiomyocytes the scientists used in this experiment), where it will ideally bind to histidine and form the potent intracellular buffer and anti-oxidant carnosine. And secondly, your body can mimic Jong, Azuma & Schaffer, who added 5mM of taurine to the solution. Now, with one molecule of taurine "buffering" each of the beta alanine molecules, the negative effects of beta alanine on the electron transport chain were blocked.

As I have emphasized before, observations like these should make you reconsider the usefulness of isolated nutrient supplementation. Our understanding of the complex regulatory mechanisms and interaction that are taking place in our bodies are still very limited. Especially long term (or high dose) effects of many "supplements" (including amino acids, vitamins, fatty acids, herbs, etc.) have not been thoroughly investigated for many of the commercially available and, as it is the case with beta alanine, scientifically backed ergogenics, nootropics, fat burners etc. Oftentimes, looking at the nutrient-complex nature has wisely attached to what we ignorantly isolated and put into a tablet or powder, would suffice to know that, an amino acid like beta alanine, which occurs naturally in relatively low doses in slowly absorbed whole foods, mostly meat products, which obviously also contain taurine, was probably not meant to be ingested at high doses in isolated powder form. Co-ingestion (not necessarily at the same time) of adequate amounts of taurine or its precursors, methionine, respectively cysteine, would thus be the imperative prerequisite to benefit from the proven ergogenic effects (esp. during high-intensity exercise) of beta alanine.
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