Passive loss of hydrogen sulfide in biological experiments

Hydrogen sulfide (H2S) 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 mu M H2S (Na2S center dot 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). H2S 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 H2S 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, H2S rapidly disappears from buffer under a variety of experimental conditions, and this is due to volatilization, not oxidation. The inability to maintain H2S concentration, even briefly, questions the accuracy of dose-response studies and the relevance of long-term (>10 min) exposure to a single treatment of H2S. These results also help to explain the discrepancy between low H2S concentrations in blood and tissues versus high concentrations of exogenous H2S required to produce physiological responses. (C) 2011 Elsevier Inc. All rights reserved.