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1 Medical College of Wisconsin, Cardiovascular Center, 2 Veterans Affairs Medical Center, and 3 Midwest Heart Surgery Institute, Milwaukee, Wisconsin 53226; and 4 Second Department of Internal Medicine, Akita University, Akita City 0108543, Japan
Thrombin (Thromb), activated as
part of the clotting cascade, dilates conduit arteries through an
endothelial pertussis toxin (PTX)-sensitive G-protein receptor and
releases nitric oxide (NO). Thromb also acts on downstream
microvessels. Therefore, we examined whether Thromb dilates human
coronary arterioles (HCA). HCA from right atrial appendages were
constricted by 30-50% with endothelin-1. Dilation to Thromb
(10
4-1 U/ml) was assessed before and after
inhibitors with videomicroscopy. There was no tachyphylaxis to Thromb
dilation (maximum dilation = 87.0%, ED50 = 1.49 × 10
2). Dilation to Thromb was abolished with
either hirudin or denudation but was not affected by PTX. Neither
N
-nitro-L-arginine methyl ester
(n = 7), indomethacin (n = 9), 1H-[1,2,4]
oxadiazolo-[4,3-a]quinoxalin-1-one (n = 6),
tetraethylammonium chloride (n = 5), nor iberiotoxin
(n = 4) reduced dilation to Thromb. However, KCl
(maximum dilation = 89 ± 5 vs. 20 ± 10%; P < 0.05; n = 7), tetrabutylammonium
chloride (maximum dilation = 79 ± 7 vs. 21 ± 4%;
P < 0.05; n = 5), and charybdotoxin
(maximum dilation = 89 ± 4 vs. 10 ± 2%;
P < 0.05; n = 4) attenuated dilation to Thromb. In contrast to animal models, Thromb-induced dilation in
human arterioles is independent of Gi-protein activation
and NO release. However, Thromb dilation is endothelium dependent, is
maintained on consecutive applications, and involves activation of
K+ channels. We speculate that an endothelium-derived
hyperpolarizing factor contributes to Thromb-induced dilation in HCA.
coronary circulation; coronary disease; K+ channel; vasoactive agent
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