1. Modulation of Na+/alanine cotransport in liver sinusoidal membrane vesicles by internal divalent cations
- Author
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Department of Medicine, University of Michigan School of Medicine and Veterans Administration Medical Center, Ann Arbor, MI, U.S.A., Department of Biophysics, Environmental Health Sciences Center, University of Rochester School of Medicine, Rochester, NY, U.S.A., Department of Medicine and Liver Center, Yale University School of Medicine, New Haven, CT, U.S.A., Simmons, Thomas W., Moseley, Richard H., Boyer, James L., Ballatori, Nazzareno, Department of Medicine, University of Michigan School of Medicine and Veterans Administration Medical Center, Ann Arbor, MI, U.S.A., Department of Biophysics, Environmental Health Sciences Center, University of Rochester School of Medicine, Rochester, NY, U.S.A., Department of Medicine and Liver Center, Yale University School of Medicine, New Haven, CT, U.S.A., Simmons, Thomas W., Moseley, Richard H., Boyer, James L., and Ballatori, Nazzareno
- Abstract
Rat liver basolateral plasma membrane (bILPM) vesicles resuspended in 5 mM Mg2+-, Ca2+-, Mn2+- or Co2+-containing media exhibited a markedly lower rate of Na+-stimulated -alanine transport. Divalent cation inhibition of -alanine uptake was dose dependent, and was observed only when the vesicles were pre-loaded with the divalent cations. The presence or absence of the metal ions in the extravesicular incubation media had no effect on -alanine transport. Conversely, pretreatment of the vesicles with 0.2 mM of either EGTA or EDTA resulted in higher initial rates of -alanine transport. This stimulation was overcome by addition of excess divalent cation to the vesicle suspension solution. Since these bILPM vesicles are primarily oriented right-side-out, the divalent cation inhibition of -alanine transport appears to be a result of their interaction with cytosolic components of the cell membrane. Total Na+ flux as measured with 22Na+ was not affected by intravesicular 5 mM Mg2+ or Ca2+, indicating that the inhibition was not due to dissipation of the Na+ gradient. These observations suggest that intracellular divalent cations may serve to modulate -alanine transport across the liver cell plasma membrane.
- Published
- 2006