Molecular and Cellular Endocrinology 251 (2006) 49–55 E-NTPDase 3 (ATP diphosphohydrolase) from cardiomyocytes, activity and expression are modulated by thyroid hormone Maria Luiza M. Barreto-Chaves a,∗ , Marcela Sorelli Carneiro-Ramos b , Guilherme Cotomacci a , Marconi Barbosa Coutinho J ´ unior a , Jo˜ ao Jos´ e Freitas Sarkis c a Laboratory of Cellular Biology and Functional Anatomy, Department of Anatomy, Biomedical Sciences Institute, University of S˜ ao Paulo, Av. Prof. Lineu Prestes 2415, Cidade Universit´ aria, S ˜ ao Paulo, SP 05508-900, Brazil b Department of Cell and Developmental Biology, Instituto de Ciˆ encias Biom´ edicas, University of S˜ ao Paulo, SP, Brazil c Department of Biochemistry, Instituto de Ciˆ encias B ´ asicas da Sa ´ ude, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil Received 31 October 2005; received in revised form 12 January 2006; accepted 20 February 2006 Abstract Degradation of adenine nucleotides by myocardial cells occurs, in part, by a cascade of surface-located enzymes converting ATP into adenosine that has important implications for the regulation of the nucleotide/nucleoside ratio modulating the cardiac functions. Thyroid hormones have profound effects on cardiovascular system, as observed in hypo- and hyperthyroidism. Combined biochemical parameters and gene expression analysis approaches were used to investigate the influence of tri-iodothyronine (T3) on ATP and ADP hydrolysis by isolated myocytes. Cultures of cardiomyocytes were submitted to increasing doses of T3 for 24 h. Enzymatic activity and expression were evaluated. T3 (0.1 nM) caused an increase in ATP and ADP hydrolysis. Experiments with specific inhibitors suggest the involvement of an NTPDase, which was confirmed by an increase in NTPDase 3 messenger RNA (mRNA) levels. Since T3 promotes an increase in the contractile protein, leading to cardiac hypertrophy, it is tempting to postulate that the increase in ATP hydrolysis and the decrease in the extracellular levels signify an important factor for prevention of excessive contractility. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: NTPDase 2; NTPDase 3; Adenosine; Thyroid hormone; Ecto-nucleotidases; Cardiomyocytes 1. Introduction Adenosine is the final product of the hydrolysis of extracellu- lar adenine nucleotides such as ATP, ADP and AMP and has been suggested to be an important vasodilator in the cardiovascular system, exerting a cardioprotective action (Tucker and Linden, 1993). Cardiomyocytes and vascular cells readily form, trans- port and metabolize the endogenous adenosine, and at the same time regulate both interstitial and plasma concentrations of this metabolite. The adenosine could be liberated as such as from cells or the adenine nucleotides released could be metabolized and rapidly converted to adenosine through the action of the ecto- enzymes (Zimmermann, 2001). The cascade of ecto-enzymes for this purpose is formed by an NTPDase (ATP diphosphohy- drolase, EC 3.6.1.5) that can hydrolyze ATP and ADP to AMP ∗ Corresponding author. Tel.: +55 11 3815 9695; fax: +55 11 3091 7366. E-mail address: mchaves@usp.br (M.L.M. Barreto-Chaves). and by a 5 ′ -nucleotidase (EC 3.1.3.5) that hydrolyzes AMP to the end product, adenosine. The presence of this enzyme cascade has been well demonstrated in vegetable and animal tis- sues (Oses et al., 2004). In addition, ecto-nucleotidases able to hydrolyze ATP–ADP–AMP are also present in the heart (Borst and Schrader, 1991). Bowditch et al. (1985) first demonstrated that rat cardiomyocytes are able to hydrolyze extracellular ATP, ADP and AMP; however, the regulation of extracellular adeno- sine production by ecto-nucleotidases of adult rat ventricular myocytes was evaluated only in 1992 (Meghji et al., 1992). Since the integrated response to adenine nucleotides and adeno- sine on the heart depends on their relative concentrations and location, a full understanding of the pattern of ecto-nucleotidase activities in each different cell type within the heart is neces- sary, taking into account that these enzymes can modulate the nucleotides/nucleoside ratio. Thyroid hormones have profound effects on the cardiovascu- lar system, as demonstrated by the changes accompanying both hypo- and hyperthyroidism (Klein, 1990). Hyperthyroidism is 0303-7207/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.mce.2006.02.010