Int. J. Devl Neuroscience 22 (2004) 11–17 Inhibition of Na + ,K + -ATPase activity in rat striatum by the metabolites accumulated in Lesch–Nyhan disease Caren S. Bavaresco, Alexandra I. Zugno, Bárbara Tagliari, Clóvis M.D. Wannmacher, Moacir Wajner, Angela T.S. Wyse ∗ Departamento de Bioqu´ ımica, Instituto de Ciˆ encias Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos, 2600-Anexo, CEP 90035-003, Porto Alegre, RS, Brazil Received 10 October 2003; received in revised form 18 November 2003; accepted 20 November 2003 Abstract In the present study, we investigated the in vitro effect of hypoxanthine, xanthine and uric acid, metabolites accumulating in tissue of patients with Lesch–Nyhan disease, on Na + ,K + -ATPase activity in striatum of neonate rats. Results showed that all compounds significantly inhibited Na + ,K + -ATPase activity. We also studied the kinetics of the inhibition of Na + ,K + -ATPase activity caused by hypoxanthine. The apparent K m and V max of Na + ,K + -ATPase activity for ATP as the substrate and hypoxanthine as the inhibitor were 0.97 mM and 0.69 nmol inorganic phosphate (Pi) released per min per mg of protein, respectively. K i -value was 1.9 M, and the inhibition was of the non-competitive type. We also observed that the inhibitory effects of hypoxanthine, xanthine and uric acid probably occur through the same mechanism, suggesting a common binding site for these oxypurines on Na + ,K + -ATPase. Therefore, it is conceivable that inhibition of brain Na + ,K + -ATPase activity may be involved at least in part in the neuronal dysfunction characteristic of patients with Lesch–Nyhan disease. © 2003 ISDN. Published by Elsevier Ltd. All rights reserved. Keywords: Na + ,K + -ATPase; Lesch–Nyhan; Hypoxanthine; Xanthine; Uric acid; Striatum 1. Introduction Lesch–Nyhan disease is an inherited metabolic disorder of purine metabolism caused by a severe deficiency on hypoxanthine–guanine phosphoribosyl-transferase (HPRT) activity, resulting in tissue accumulation of hypoxanthine, xanthine and uric acid. This enzyme recycles hypoxanthine and guanine into inosine monophosphate (IMP) and gua- nine monophosphate (GMP), respectively (Fig. 1). It has been demonstrated that the highly expressed HPRT activity, particularly the basal ganglia, is important to the purine salvage pathway in order to maintain adequate purine lev- els (Visser et al., 2000; Jinnah and Friedmann, 2001). In most tissues, hypoxanthine, the major metabolite accumu- lated in Lesch–Nyhan disease, is predominantly degraded to xanthine and uric acid (Visser et al., 2000). Affected patients with Lesch–Nyhan disease present hy- peruricemia, spasticity, dystonia, mental retardation and a self-mutilation behavior, which is characterized by biting of ∗ Corresponding author. Tel.: +55-51-3316-5573; fax: +55-51-3316-5535. E-mail address: wyse@ufrgs.br (A.T.S. Wyse). the lips, tongue and fingers with apparent tissue loss (Jinnah et al., 1990). Alteration of the dopamine transmitter system in basal ganglia of these patients is also observed (Jinnah and Friedmann, 2001). Although the underlying mechanisms of brain dysfunction in Lesch–Nyhan disease are poorly understood, the accumu- lation of oxypurines is believed to contribute to the neurolog- ical damage characteristic of this disease. In this context, it has been demonstrated that hypoxanthine and xanthine bind to brain benzodiazepinic receptors, interfering with their nor- mal function (Ticku and Burch, 1980). In addition, Palmour et al. (1989) showed that hypoxanthine provokes dopamine depletion in cultured neuronal cells. Interestingly, high lev- els of hypoxanthine are found in some neuropathologies, including hydrocephalus (Schmidt et al., 1995) and cerebral ischemia (Hagberg et al., 1987). Furthermore, brain edema, probably mediated by oxidative stress, can be elicited by exposing the CNS to xanthine and xanthine oxidase (Chan et al., 1984). On the other hand, it has been proposed that xanthines derivatives, such as methylxanthines, induce seizures in rat (Cutrufo et al., 1992; Mares et al., 1994). Na + ,K + -ATPase (EC 3.6.1.37) is an enzyme embed- ded in the cell membrane, responsible for the generation 0736-5748/$30.00 © 2003 ISDN. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijdevneu.2003.11.002