Aims: 

Conducted dilation occurs in both the microcirculation and small resistance arteries. Any agonist that stimulates smooth muscle cell hyperpolarization has the potential to be associated with conducted dilation, and thereby influence blood flow. We aimed to study whether adenosine triphosphate (ATP) can evoke conducted dilation following either luminal or extraluminal application.

Methods: 

Arteries were dissected with a bifurcation, cannulated and tied onto glass pipettes. Using a confocal microscope we simultaneously imaged the feed artery and the bifurcation vessels. ATP or ACh together with carboxyfluorescein were luminally perfused into one branch of the bifurcation (Branch-1) and continuous flow through the feed vessel prevented upstream diffusion of agonists and dye. The inner diameter of the vessel at 500mm increments upstream from the bifurcation, as well as that in Branch-1 were measured offline using Imaris software (Bitplane). The responses to both agonists were expressed relative to the 80% maximal dilatation at the 0 mm position in the feed artery. Endothelial cell Ca²⁺ imaging was performed following luminal perfusion of Oregon Green BAPTA-1 AM.

Results: 

The maximum diameter of the feed arteries was 175±3mm at the position 500mm upstream, and 158±3mm in Branch-1 (n=5). Arteries developed approximately 40% tone. Luminal perfusion of 10mM ATP stimulated rapid dilatation of both Branch-1 and the feed artery. ATP stimulated 89±6% dilatation in Branch-1, and 82±3, 73±6, and 68±10% dilatation, at the 0, 500, 1000mm positions respectively (n=5). These responses were unaltered by the NO synthase inhibitor L-NAME (100mM, n=5), and the response to luminal ACh (3 mM) was also not different (n=5). Luminal perfusion of ATP increased endothelial cell Ca²⁺. Focal pipette application of ATP (10mM) extraluminally caused a biphasic response, local and conducted constriction followed by dilatation.

Conclusions: 

Thus in rat cremaster arteries ATP can evoke conducted contraction and dilation, but when delivered luminally, dilation is the predominant pathway. Furthermore, luminal perfusion of ATP evokes dilatation that is associated with increases in endothelial cell Ca²⁺.