RESUMEN
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.
Asunto(s)
Adenosina Difosfato/análogos & derivados , Cuerpo Estriado/efectos de los fármacos , Cuerpo Estriado/metabolismo , Fosfatos de Dinucleósidos/metabolismo , Fosfatos de Dinucleósidos/farmacología , Ácido Glutámico/metabolismo , Receptores Purinérgicos P2/metabolismo , Adenosina Difosfato/metabolismo , Animales , Relación Dosis-Respuesta a Droga , Espacio Extracelular/efectos de los fármacos , Espacio Extracelular/metabolismo , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Masculino , Neurotransmisores/farmacología , Ratas , Ratas Wistar , Tionucleótidos/metabolismoRESUMEN
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.
Asunto(s)
Ácido Anhídrido Hidrolasas/sangre , Ácido Anhídrido Hidrolasas/metabolismo , Proteínas de Neoplasias , Proteínas/metabolismo , Ácido Anhídrido Hidrolasas/química , Ácido Anhídrido Hidrolasas/aislamiento & purificación , Calcio/farmacología , Cationes Bivalentes/farmacología , Cromatografía en Gel , Cromatografía Líquida de Alta Presión , Humanos , Cinética , Magnesio/farmacología , Manganeso/farmacología , Proteínas/química , Proteínas/aislamiento & purificación , Espectrometría de Fluorescencia , Zinc/farmacologíaRESUMEN
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.
Asunto(s)
Ácido Anhídrido Hidrolasas/antagonistas & inhibidores , Inhibidores Enzimáticos/farmacología , Proteínas de Neoplasias , Hidrolasas Diéster Fosfóricas/metabolismo , Suramina/farmacología , Animales , Encéfalo/metabolismo , Fosfatos de Dinucleósidos/metabolismo , Hidrólisis , Masculino , Inhibidores de Fosfodiesterasa/farmacología , Ratas , Ratas Wistar , Extractos de TejidosRESUMEN
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.
