Hormonal stimulation of Mg2+ uptake in hepatocytes. Regulation by plasma membrane and intracellular organelles.
Collagenase dispersed rat liver hepatocytes release Mg2+ when stimulated with norepinephrine or accumulate Mg2+ when stimulated with vasopressin, respectively. Mg2+ fluxes in either direction account for a net loss or gain of approximately 10% of total cell magnesium and are rapidly reversible. Both stimulated Mg2+ efflux and Mg2+ influx require physiological concentration of extracellular NaCl and Ca2+. In the absence of extracellular Na+, Mg2+ efflux, but not influx, can be observed in the presence of extracellular Cl-. Under these conditions, the efflux is inhibited by the Cl-/HCO3- exchanger inhibitor 4,4'-dinitrostilbene-2,2'-disulfonic acid. In hepatocytes, Mg2+ influx, but not efflux, is completely inhibited by thapsigargin, a specific inhibitor of the endoplasmic reticulum Ca2+ ATPase. Several lines of evidence, such as measurements of cytosolic Ca2+ or of cytosolic Ca2+ buffering, indicate that the effect of thapsigargin in inhibiting Mg2+ influx could not be explained by an increase in cytosolic Ca2+. Instead, the inhibition of hepatocyte Mg2+ influx was found to be the result of the depletion of the Ca2+ stored within the endoplasmic reticulum.
Romani
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Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
Marfella
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Scarpa
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D000818:Animals; D001692:Biological Transport; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006728:Hormones / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D015388:Organelles / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin
D002712:Chlorides; D006728:Hormones; D013729:Terpenes; D004533:Egtazic Acid; D019284:Thapsigargin; D012964:Sodium; D000252:Calcium-Transporting ATPases; D008274:Magnesium; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D013755:Tetradecanoylphorbol Acetate; D009638:Norepinephrine