Conducted dilation to intra‐ and extraluminal application of ATP in rat cremaster arteries

ATP can evoke contraction or dilation of arteries depending on the cell‐type activated. The ability of ATP to evoke local and spreading dilation was studied in isolated rat cremaster arteries which were cannulated, heated to 34–35°C, and pressurized to 70 mmHg. In all cases carboxyfluorescein was added to the ATP solutions, and fluorescence and diameter measured simultaneously along the length of vessels (at least 1000 μm) using confocal microscopy. In some experiments, endothelial cells were loaded with a fluorescent Ca2+ indicator. Against myogenic tone, luminal perfusion of 10μM ATP into one branch and out the other at a bifurcation stimulated rapid and robust dilation of the branches, which conducted upstream into the feed artery with little decay. The responses to ATP were associated with increased endothelial cell Ca2+, were unaltered by the NO synthase inhibitor L‐NAME, but abolished by K+ channel blockers, and were similar to that of ACh (3μM). Focal pipette application of ATP (10μM) extraluminally caused a biphasic response, local and conducted constriction followed by dilatation. These findings show that in rat cremaster arteries ATP can evoke conducted contraction and dilation, but when delivered luminally, dilation is the predominant pathway. Supported by British Heart Foundation and Wellcome Trust.