RESUMO
Our aim was to investigate the neuromodulatory role of diadenosine tetraphosphate (Ap(4)A). Ap(4)A-binding sites were detected in striatum and hippocampus membranes using [(35)S]-ADP beta S as radioligand and Ap(4)A and epsilon-(Ap(4)A), di-ethenoadenosine tetraphosphate, as displacers. Effects of epsilon-(Ap(4)A) on extracellular glutamate levels were studied using intracerebral perfusion. Both areas contain high-affinity binding sites for [(35)S]-ADP beta S with K(d) values in the low nM range. [(35)S]-ADP beta S binding was displaced by Ap(4)A and epsilon-(Ap(4)A). At 1 and 10 microM doses, epsilon-(Ap(4)A) markedly decreased glutamate levels in the striatum. The possibility of Ap(4)A acting as an endogenous modulator of excitatory neurotransmission is discussed.
Assuntos
Difosfato de Adenosina/análogos & derivados , Corpo Estriado/efeitos dos fármacos , Corpo Estriado/metabolismo , Fosfatos de Dinucleosídeos/metabolismo , Fosfatos de Dinucleosídeos/farmacologia , Ácido Glutâmico/metabolismo , Receptores Purinérgicos P2/metabolismo , Difosfato de Adenosina/metabolismo , Animais , Relação Dose-Resposta a Droga , Espaço Extracelular/efeitos dos fármacos , Espaço Extracelular/metabolismo , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Masculino , Neurotransmissores/farmacologia , Ratos , Ratos Wistar , Tionucleotídeos/metabolismoRESUMO
Human platelets diadenosine triphosphatase was characterised and compared with the Fhit protein, a human tumour suppressor with diadenosine triphosphatase activity. Both enzymes exhibit similar Km, are similarly activated by Mg2+, Ca2+ and Mn2+, and inhibited by Zn2+ and suramin. However, they are differentially inhibited by Fhit antibodies and exhibit differences in gel-filtration behaviour.
Assuntos
Hidrolases Anidrido Ácido/sangue , Hidrolases Anidrido Ácido/metabolismo , Proteínas de Neoplasias , Proteínas/metabolismo , Hidrolases Anidrido Ácido/química , Hidrolases Anidrido Ácido/isolamento & purificação , Cálcio/farmacologia , Cátions Bivalentes/farmacologia , Cromatografia em Gel , Cromatografia Líquida de Alta Pressão , Humanos , Cinética , Magnésio/farmacologia , Manganês/farmacologia , Proteínas/química , Proteínas/isolamento & purificação , Espectrometria de Fluorescência , Zinco/farmacologiaRESUMO
The cytosolic enzymes asymmetrical diadenosine tetraphosphate hydrolase (EC 3.6.1.17, Ap4Aase) and diadenosine triphosphate hydrolase (EC 3.6.1.29, Ap3Aase) are inhibited competitively by suramin. Ap4Aase and Ap3Aase were assayed in cytosolic rat brain extracts using fluorogenic analogues of the respective substrates diadenosine tetraphosphate (Ap4A) and diadenosine triphosphate (Ap3A). Ki values for suramin as inhibitor of Ap4Aase and Ap3Aase were 5 x 10(-6) M and 3 x 10(-7) M, respectively. Results indicate that suramin or suramin-like derivatives may be useful tools to investigate diadenosine polyphosphate cleaving enzymes and that the intracellular diadenosine polyphosphate metabolism may be a pharmacological target of suramin with biological and clinical implications.
Assuntos
Hidrolases Anidrido Ácido/antagonistas & inibidores , Inibidores Enzimáticos/farmacologia , Proteínas de Neoplasias , Diester Fosfórico Hidrolases/metabolismo , Suramina/farmacologia , Animais , Encéfalo/metabolismo , Fosfatos de Dinucleosídeos/metabolismo , Hidrólise , Masculino , Inibidores de Fosfodiesterase/farmacologia , Ratos , Ratos Wistar , Extratos de TecidosRESUMO
The values of low-density lipoprotein cholesterol obtained according to the Friedewald formula (Clin Chem 1972; 18:499-502), or by the De Long transformation (J Am Med Assoc 1986;256:2372-7), were compared with the values obtained when the individual cholesterol/triglyceride ratio of very-low-density lipoprotein was used for estimating the contribution of this lipoprotein to the total cholesterol. We found that these formulas gave the greatest errors for individuals with a low serum cholesterol/triglyceride ratio. We propose criteria for deciding when the numerically calculated value of low-density cholesterol is appropriate, and when it is not.
