Aluminum-induced alterations in [3H]Ouabain binding and ATP hydrolysis catalyzed by the rat brain synaptosomal (Na+ + K+)-ATPase°

Abstract

The (Na(+)+K+)-ATPase is responsible for maintenance of the ionic milieu of cells. The objective of this study is to investigate the effect of aluminum, an ion implicated in several neurological disorders, on ATP hydrolysis catalyzed by the rat brain synaptosomal (Na(+)+K+)-ATPase and on the binding of [3H]ouabain to this enzyme. AlCl3 (25-100 microM) inhibits the phosphatase activity of the (Na(+)+K+)-ATPase in a dose-dependent manner. AlCl3 appears to act as a reversible, noncompetitive inhibitor of (Na(+)+K+)-ATPase activity by decreasing the maximum velocity of the enzyme without significantly affecting the apparent dissociation constant with respect to ATP. AlCl3 may affect Mg2+ sites on the (Na(+)+K+)-ATPase but does not appear to interact with Na+ or K+ sites on the enzyme. In contrast to this inhibitory effect on the phosphatase function of the enzyme, AlCl3 (1-100 microM) stimulates the binding of [3H]ouabain to the (Na(+)+K+)-ATPase. This effect is due to an increase in the maximum [3H]ouabain binding capacity of the enzyme with no change in the [3H]ouabain binding affinity. These data support the hypothesis that AlCl3 may stabilize the phosphorylated form of the synaptosomal (Na(+)+K+)-ATPase which increases [3H]ouabain binding while inhibiting the phosphatase activity of the enzyme.

Comparative effects of aluminum and ouabain on synaptosomal choline uptake, acetylcholine release and (Na+/K+)ATPase

“…The sensitivity of rat brain (Na + /K + )ATPase to AlCl 3 at submillimolar concentrations has previously been shown (King et al, 1983;Rao, 1990Rao, , 1992Caspers et al, 1993Caspers et al, , 1994Silva and Gonçalves, 2003;Silva et al, 2005). Accordingly, the hemicholinium-3-sensitive [ 3 H]choline uptake by rat synaptosomes was inhibited by AlCl 3 (Fig.…”

“…Several studies have cast some doubt on cholinergic hypothesis of aluminum neurotoxicity, both with respect to metabolism of acetylcholine (i.e., Marquis and Black, 1984;Kaizer et al, 2005) and with respect to choline and acetylcholine translocation across presynaptic nerve terminals (i.e., Sirvio et al, 1988;Amador et al, 2001). One possibility, supported by the observation that aluminum inhibits the mammalian (Na + /K + )ATPase activity (Lai et al, 1980;King et al, 1983;Rao, 1990Rao, , 1992Caspers et al, 1993Caspers et al, , 1994Lal et al, 1993;Sarin et al, 1997;Silva and Gonçalves, 2003;Silva et al, 2005), is that aluminum impairs choline uptake and acetylcholine release by inhibiting (Na + /K + )ATPase rather than by direct interaction with uptake and release machinery. The presumptive role of aluminum-induced (Na + /K + )ATPase inhibition on choline and acetylcholine translocation across presynaptic nerve terminals has been challenged in this study.…”

“…The high-affinity choline transport by cholinergic presynaptic nerve terminals is hemicholinium-3-sensitive (K i ≈ 10 −9 to 10 −7 M) and driven by the transmembrane Na + gradient (Kuhar and Zarbin, 1978;Vickroy et al, 1985;Chatterjee et al, 1987;Saltarelli et al, 1987;Happe and Murrin, 1993;Okuda et al, 2000;Misawa et al, 2001), which is maintained by the (Na + /K + )ATPase (Stein, 1990;Nelson and Lill, 1994). During the last 20 years, a number of reports appeared to emphasize that in vivo and in vitro exposure of mammalian preparations to aluminum inhibits this P-type ATPase, a ubiquitous integral membrane pump of the plasma membrane (Lai et al, 1980;King et al, 1983;Rao, 1990Rao, , 1992Caspers et al, 1993Caspers et al, , 1994Lal et al, 1993;Sarin et al, 1997;Silva and Gonçalves, 2003;Silva et al, 2005).…”

Melatonin Prevents Oxidative Stress in Ovariectomized Rats Treated with Aluminium

“…Likewise, the Na + -K + -ATPase pump is expressed in the basolateral membrane of hepatocytes and generates a sodium gradient that allows passive diffusion of other substances inside the cells [34]. The inhibitory effect of in vivo and in vitro exposure to Al on the Na + -K + -ATPase activity has been observed by several investigators although the cause of this remains controversial [35][36][37][38]. Melatonin (Mel: N-acetyl-5-methoxytryptamine) is naturally produced in the pineal gland from serotonin through a process catalyzed by two enzymes: arylalkylamine-Nacetyltransferase and hydroxindole-O-methyltransferase.…”

Effect of long‐term exposure to aluminum and high‐fat diet on NTPDase and 5′‐nucleotidase activities in lymphocytes and platelets of rats

“…This can be facilitated for the alteration in the integrity of cellular membranes, which consequently can affect the conformation of the enzyme (Schetinger et al., ). Also, the ability of Al–ATP to stabilize intermediates such as enzyme‐substrate complexes is well known (Caspers, Dow, Fu, Jacques, & Kwaiser, ). In this case, the NTPDase and 5′‐nucleotidase enzymes presented a significant increase of the activities in response to the aluminum plus high‐fat‐diet treatments.…”