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1Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia; and 2Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin
Submitted 7 October 2005 ; accepted in final form 27 January 2006
The present study was designed to determine the production of nicotinic acid adenine dinucleotide phosphate (NAADP) and its role associated with lysosomes in mediating endothelin-1 (ET-1)-induced vasoconstriction in coronary arteries. HPLC assay showed that NAADP was produced in coronary arterial smooth muscle cells (CASMCs) via endogenous ADP-ribosyl cyclase. Fluorescence microscopic analysis of intracellular Ca2+ concentration ([Ca2+]i) in CASMCs revealed that exogenous 100 nM NAADP increased [Ca2+]i by 711 ± 47 nM. Lipid bilayer experiments, however, demonstrated that NAADP did not directly activate ryanodine (Rya) receptor Ca2+ release channels on the sarcoplasmic reticulum. In CASMCs pretreated with 100 nM bafilomycin A1 (Baf), an inhibitor of lysosomal Ca2+ release and vacuolar proton pump function, NAADP-induced [Ca2+]i increase was significantly abolished. Moreover, ET-1 significantly increased NAADP formation in CASMCs and resulted in the rise of [Ca2+]i in these cells with a large increase in global Ca2+ level of 1,815 ± 84 nM. Interestingly, before this large Ca2+ increase, a small Ca2+ spike with an increase in [Ca2+]i of 529 ± 32 nM was observed. In the presence of Baf (100 nM), this ET-1-induced two-phase [Ca2+]i response was completely abolished, whereas Rya (50 µM) only markedly blocked the ET-1-induced large global Ca2+ increase. Functional studies showed that 100 nM Baf significantly attenuated ET-1-induced maximal constriction from 82.26 ± 4.42% to 51.80 ± 4.36%. Our results suggest that a lysosome-mediated Ca2+ regulatory mechanism via NAADP contributes to ET-1-induced Ca2+ mobilization in CASMCs and consequent vasoconstriction of coronary arteries.
-nicotinamide adenine dinucleotide phosphate; adenosine 5'-diphosphate-ribosyl cyclase; coronary artery; vascular smooth muscle
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