FIG. 6.
Inverse correlation between H2S and O2 in biological tissues. (A) Simultaneous measurement of H2S and O2 concentrations in homogenized rat lung measured in real-time with H2S and O2 polarographic electrodes. H2S is produced in the presence of precursors of H2S biosynthesis, cysteine and α-ketoglutarate, and in the absence of O2. Injection of a small air bubble (arrow) increases O2 concentration and immediately decreases H2S concentration. H2S production resumes after the O2 is consumed. Modified from Olson and Whitfield (56); (B) Solid lines show O2-dependent H2S consumption by pulmonary arterial smooth muscle cells (PASMC), homogenized bovine lung (lung), and purified mitochondria (mito) compared with O2 dependence of hypoxic pulmonary vasoconstriction of isolated bovine pulmonary arteries (vessel; dashed line). Percent activity refers to the degree of H2S consumption (100%=all H2S consumed) or percentage of hypoxic contraction (100%=maximum vessel contraction). Modified from Olson et al. (57). Horizontal arrows above the figure refer to the range of Po2 in mitochondria (mito), cytosol (cyto), and tissues (tiss) reported in the literature. Half maximal H2S consumption and vessel contraction occurs at approximately the same Po2 and these Po2s are below those encountered in normoxia, i.e., hypoxic conditions.