Passive loss of hydrogen sulfide in biological experiments

Hydrogen sulfide (H(2)S) is a volatile gas of considerable interest as a physiologically relevant signaling molecule, but this volatility has typically been overlooked in the context of biological experiments. We examined volatility of 10 and 100 μM H(2)S (Na(2)S·9H(2)O) in real time with polarographic electrodes in three commonly employed experimental apparatuses: 24-well tissue culture plates (WP), muscle myograph baths (MB), and the Langendorff perfused heart apparatus (LPH). H(2)S loss from all apparatuses was rapid and exponential, with half-times (t(1/2)) of 5 min (WP), less than 4 min (MB), and less than 0.5 min (LPH). The t(1/2) for H(2)S loss from MB bubbled with 100% oxygen was slightly longer than that for MB bubbled with 100% nitrogen; both were significantly shorter than stirred but unbubbled MB (>9 min). Therefore, even without tissue, H(2)S rapidly disappears from buffer under a variety of experimental conditions, and this is due to volatilization, not oxidation. The inability to maintain H(2)S concentration, even briefly, questions the accuracy of dose-response studies and the relevance of long-term (>10 min) exposure to a single treatment of H(2)S. These results also help to explain the discrepancy between low H(2)S concentrations in blood and tissues versus high concentrations of exogenous H(2)S required to produce physiological responses.