Protein kinase a dependent phosphorylation activates mg2+ efflux in the basolateral region of the liver |
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Authors: | C Cefaratti Cristian Ruse |
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Institution: | (1) Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA |
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Abstract: | Isolated hepatocytes in physiological Na+]
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tightly maintain Mg2+]
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. Upon β-adrenergic stimulation or in the presence of permeable cAMP, hepatocytes release 5–10% (1–3 mM Mg2+) of their total Mg2+ content. However, isolated basolateral liver plasma membranes (bLPM), release Mg2+ in the presence of Na+]
o
even in the absence of catecholamine stimulation. The data indicate that a physiological brake for Mg2+ efflux is present in the hepatocyte and is removed upon cellular signaling. In contrast, this regulation “brake” is absent
in purified bLPM thus rendering them fully active. The present study was carried out to reconstruct the missing regulatory
component. Activation of Mg2+ extrusion in intact cells is consistent with cAMP dependent phosphorylation of the transporter or a regulatory protein. Treatment
of bLPM with a non-specific phosphatase such as alkaline phosphatase (AP), decreased Mg2+ efflux by 70% compared to untreated bLPM. When AP-treated bLPM were loaded with protein kinase A (PKA), and stimulated with
permeable cAMP, Mg2+ transport fully recovered. These data suggest that phosphorylation of the Na+/Mg2+ exchanger or a nearby protein activates the Mg2+ transport mechanism in hepatocytes. |
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Keywords: | β -adrenergic activation alkaline phosphatase basolateral liver plasma membranes phosphorylation protein kinase A |
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