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Functional heterogeneity of endothelial P2 purinoceptors in the cerebrovascular tree of the rat

Authors :
T. David Johnson
Robert M. Bryan
Sean P. Marrelli
Junping You
Source :
American Journal of Physiology-Heart and Circulatory Physiology. 277:H893-H900
Publication Year :
1999
Publisher :
American Physiological Society, 1999.

Abstract

The effects of stimulating P2Y1 or P2Y2 purinoceptors on the endothelium of isolated middle cerebral arteries (MCAs), third-order branches of the MCA (bMCAs), and penetrating arterioles (PAs) of the rat were studied. After pressurization and development of spontaneous tone (25% contraction), resting diameters for MCAs, bMCAs, and PAs were 203 ± 5 ( n = 50), 99 ± 2 ( n = 42), and 87 ± 2 μm ( n = 53), respectively. Luminal application of the P2Y1-selective agonist 2-methylthioadenosine 5′-triphosphate elicited dose-dependent dilations (or loss of intrinsic tone) in MCAs but not in bMCAs or PAs. The dilation in MCAs was completely blocked by removal of the endothelium or by nitro-l-arginine methyl ester (10−5 M), an inhibitor of NO synthase. Luminal application of the P2Y2-selective agonist ATP elicited dilations in MCAs, bMCAs, and PAs. Removal of the endothelium abolished the dilations in all vessel groups. Dilations in MCAs have been shown to involve both NO and endothelium-derived hyperpolarizing factor (EDHF). The dilations in bMCAs and PAs had a minor NO component and prominent EDHF component; that is, 1) the dilations to ATP were not diminished by the combined inhibition of NO synthase and cyclooxygenase, 2) the dilations were accompanied by significant hyperpolarizations of the vascular smooth muscle (∼15 mV), and 3) the dilations were completely abolished by the calcium-activated potassium channel blocker charybdotoxin. We concluded that the role of NO in purinoceptor-induced dilations diminishes along the cerebrovascular tree in the rat, whereas the role of EDHF becomes more prominent.

Details

ISSN :
15221539 and 03636135
Volume :
277
Database :
OpenAIRE
Journal :
American Journal of Physiology-Heart and Circulatory Physiology
Accession number :
edsair.doi.dedup.....ab614037e93ab088ca21103485003443
Full Text :
https://doi.org/10.1152/ajpheart.1999.277.3.h893