An Endogenous Na+, K+-ATPase Inhibitor Enhances Phosphoinositide Hydrolysis in Neonatal but Not in Adult Rat Brain Cortex |
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Authors: | Calviño M. A. Peña C. Rodríguez de Lores Arnaiz G. |
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Affiliation: | (1) Instituto de Biología Celular y Neurociencias Prof. E. De Robertis , PROBICENE-CONICET, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, 1121 Buenos Aires, Argentina;(2) Cátedra de Farmacología, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina;(3) IQUIFIB, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina |
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Abstract: | The effect of an endogenous Na+, K+-ATPase inhibitor, termed endobain E, on phosphoinositide hydrolysis was studied in rat brain cortical prisms and compared with that of ouabain. As already shown for ouabain, a transient effect was obtained with endobain E; maximal accumulation of inositol phosphates induced by endobain E was 604 ± 138% and 186 ± 48% of basal values in neonatal and adult rats, respectively. The concentration-response plot for the interaction between endobain E and phosphoinositide turnover differed from that of ouabain, thus suggesting the involvement of distinct mechanisms. In the presence of endobain E plus ouabain at saturating concentrations, no additive effect was recorded, suggesting that both substances share at least a common step in their activation mechanism of inositol phosphates metabolism or that they enhance phosphatidylinositol 4,5-biphosphate breakdown from the same membrane precursor pool, until its exhaustion. Experiments with benzamil, a potent blocker of Na+/Ca2+ exchanger, showed that it partially and dose-dependently inhibited endobain E effect. These results indicate that the endogenous Na+, K+-ATPase inhibitor endobain E, like ouabain, is able to stimulate phosphoinositide turnover transiently during postnatal brain development. |
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Keywords: | Inositol phosphate Na+, K+-ATPase ouabain-like substance neonatal brain cortex Na+/Ca2+ exchanger |
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