Figure 1. Effects of H₂O₂ on arterioles isolated from skeletal muscle and heart.

H₂O₂ (1 µM–10 mM) was added to isolated, cannulated, skeletal muscle (initial diameter (id: 191±17 µm, n = 6 arterioles from 6 different animals) or coronary arterioles (id: 110±18 µm, n = 7 arterioles from 7 different animals) with intact endothelium. The arteriolar diameter was recorded and concentration-response (cumulative application) relationships were determined (panel A). Changes in relative arteriolar diameter are shown. Relative diameter changes during vasodilations were expressed as percentages of the difference between the maximum passive diameter (maximum dilation: 100%, determined in the absence of extracellular Ca²⁺) and initial diameter with positive values, while during constrictions they were expressed relative to the initial diameter (illustrated at 0% on the y axis) with negative values. Asterisks denote significant differences from the initial values. The kinetics of H₂O₂-evoked responses was studied in isolated skeletal muscle arterioles (panel B; means±SEM with solid and dashed lines, respectively). The effects of the indicated concentrations of H₂O₂ were recorded for 600 s in the continuous presence of H₂O₂ (n = 3–5 arterioles at each concentration from 11 different animals). The positions of maximum constrictions and dilations are illustrated by arrows.