RESUMO
Using the radioisotope method, the Ca2+ transport through proteoliposomes was investigated. The proteoliposomes originating from total brain lipids and skeletal muscle T-system membranes of the rabbit were shown to possess a Ca2+ permeability which can be stimulated by 1.4-dihydroxypyridine derivatives (10(-9)-10(-7) M). Verapamil and Cd2+ (10(-5) M and 10(-3) M, respectively) inhibit the Ca2+ permeability of proteoliposomes stimulated by dihydroxypyridine derivatives. The activating effect of the latter depends on the microviscosity of the proteoliposome lipid bilayer. An addition of cholesterol to brain phospholipids at a ratio of 1:5 increases the stimulating effect of dihydroxypyridine by 50%.
Assuntos
Bloqueadores dos Canais de Cálcio/farmacologia , Cálcio/metabolismo , Músculos/metabolismo , Proteolipídeos/metabolismo , Animais , Transporte Biológico/efeitos dos fármacos , Química Encefálica , Cádmio/farmacologia , Di-Hidropiridinas/farmacologia , Técnicas In Vitro , Membranas/metabolismo , Permeabilidade , CoelhosAssuntos
Canais de Cálcio/metabolismo , Di-Hidropiridinas/farmacologia , Lipossomos , Receptores Nicotínicos/isolamento & purificação , Animais , Transporte Biológico , Canais de Cálcio/efeitos dos fármacos , Técnicas In Vitro , Nitrendipino/farmacologia , Coelhos , Receptores Nicotínicos/efeitos dos fármacos , Receptores Nicotínicos/metabolismoRESUMO
A procedure for incorporation of isolated cattle brain Na,K-ATPase into erythrocyte membranes by proteoliposomes has been elaborated. The Na,K-ATPase activity of proteoliposome-treated human erythrocytes containing incorporated Na,K-ATPase does not exceed that of control erythrocytes. In the erythrocyte membrane the incorporated enzyme exists in a functionally active state and retains the vector properties of the Na+-pump. Exogenous ATP stimulates 22Na influx and 86Rb efflux in and from the erythrocytes.
Assuntos
Encéfalo/enzimologia , Eritrócitos/enzimologia , Canais Iônicos , Lipossomos/administração & dosagem , ATPase Trocadora de Sódio-Potássio/sangue , Sódio/sangue , Animais , Transporte Biológico Ativo , Bovinos , Membrana Eritrocítica/enzimologia , Humanos , Radioisótopos , RubídioRESUMO
Reconstitution of purified lubrol-solubilized preparation of Na,K-ATPase from the calf brain was performed in liposomes and transport characteristics of this system were investigated. The system was demonstrated to preserve vectoral features of the sodium pump. Addition of ATP to the medium evoked active influx of sodium and efflux of rubidium in proteoliposomes. Ouabain inhibited transport processes when enclosed into proteoliposomes, i.e. from the side opposite to the ATP-sensitive one.
Assuntos
Lipossomos , ATPase Trocadora de Sódio-Potássio , Sódio/metabolismo , Animais , Química Encefálica , Bovinos , Permeabilidade da Membrana Celular , Ouabaína , Fosfatidilcolinas , Fosfatidilserinas , Rubídio/metabolismo , ATPase Trocadora de Sódio-Potássio/isolamento & purificaçãoRESUMO
A mechanism of K-insensitive, ouabain-dependent liberation of Na+ from the cell during an increase in ADP intracellular concentration is studied. It is shown that the increase in the ADP/ATP ratio does not change the Na+, K+-ATPase affinity to K+ ions and does not result in the Na-activated, K-independent ATPase reaction. ADP protects ATPase from the inhibition by ouabain which is accounted for by a decrease in the concentration of a glycoside-sensitive form of the enzyme E2-P due to a turnover of the phosphokinase step of the reaction, but not due to the binding of free Mg2+ ions. The results obtained suggest that the increase in ADP concentration within the cell activates Na-Nan exchange along Na-transporting channels of the ionic pump.