Fig. 8.

Concentrations of H₂S in rodent hearts from the literature. Concentrations are expressed in micromoles per kilogram. Whenever data were expressed per gram of protein, we assumed a 10% ratio between the weight of the heart and the weight of proteins (28, 48). Free H₂S, H₂S produced in reducing environment, and H₂S released in very acidic condition were identified according to the methods used in each paper. H₂S concentrations from references a, b, and c are the concentrations measured in the present study in control, CS, and CA conditions, respectively. ND, undetectable. This figure shows that 2 different ranges of concentrations of free H₂S can be found in the literature (see discussion): a first group of studies including ours identified levels of free H₂S below 0.2 μmol/kg, while a second group of studies reported levels between 6,000 and 40,000 μmol/kg. Similarly very high concentrations of H₂S have been found after addition of a reducing agent, which in most cases was DTT (in contrast to TCEP in our study), corresponding to levels of H₂S even higher than the entire amount of H₂S that was administered (see also Table 1). The acid-labile H₂S concentrations are all within a similar range (high micromolar) in all studies.