HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Supplemental Figures All Versions of this Article: 296/4/C828    most recent 00619.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Prosdocimo, D. A. Articles by Dubyak, G. R. Search for Related Content PubMed PubMed Citation Articles by Prosdocimo, D. A. Articles by Dubyak, G. R.

VASCULAR BIOLOGY

Autocrine ATP release coupled to extracellular pyrophosphate accumulation in vascular smooth muscle cells

¹Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio; and ²Department of Medicine, Renal Division, Emory University School of Medicine, Atlanta, Georgia

Submitted 2 December 2008 ; accepted in final form 29 January 2009

Extracellular inorganic pyrophosphate (PP_i) is a potent suppressor of physiological calcification in bone and pathological calcification in blood vessels. Ectonucleotide pyrophosphatase/phosphodiesterases (eNPPs) generate PP_i via the hydrolysis of ATP released into extracellular compartments by poorly understood mechanisms. Here we report that cultured vascular smooth muscle cells (VSMC) from rat aorta generate extracellular PP_i via an autocrine mechanism that involves ATP release tightly coupled to eNPP activity. The nucleotide analog β,-methylene ATP (MeATP or AMPPCP) was used to selectively suppress ATP metabolism by eNPPs but not the CD39-type ecto-ATPases. In the absence of MeATP, VSMC generated extracellular PP_i to accumulate 600 nM within 2 h while steadily maintaining extracellular ATP at 1 nM. Conversely, the presence of MeATP completely suppressed PP_i accumulation while increasing ATP accumulation. Probenecid, which inhibits PP_i efflux dependent on ANK, a putative PP_i transporter or transport regulator, reduced extracellular PP_i accumulation by approximately twofold. This indicates that autocrine ATP release coupled to eNPP activity comprises 50% of the extracellular PP_i-generating capacity of VSMC. The accumulation of extracellular PP_i and ATP was markedly attenuated by reduced temperature but was insensitive to brefeldin A, which suppresses constitutive exocytosis of Golgi-derived secretory vesicles. The magnitude of extracellular PP_i accumulation in VSMC cultures increased with time postplating, suggesting that ATP release coupled to PP_i generation is upregulated as cultured VSMC undergo contact-inhibition of proliferation or deposit extracellular matrix.

adenosine 5'-triphosphate release; vascular calcification; ectonucleotide pyrophosphatase; ectoadenosine 5'-triphosphatase