Passive loss of hydrogen sulfide in biological experiments

Abstract

Hydrogen sulfide (H 2S) 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 2S (Na 2S·9H 2O) 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 2S 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 2S 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 2S rapidly disappears from buffer under a variety of experimental conditions, and this is due to volatilization, not oxidation. The inability to maintain H 2S 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 2S. These results also help to explain the discrepancy between low H 2S concentrations in blood and tissues versus high concentrations of exogenous H 2S required to produce physiological responses.