Title: Modulation of Na+/alanine cotransport in liver sinusoidal membrane vesicles by internal divalent cations.

Authors: Simmons, T W; Moseley, R H; Boyer, J L; Ballatori, N

Published In Biochim Biophys Acta, (1990 Apr 30)

Abstract: Rat liver basolateral plasma membrane (blLPM) vesicles resuspended in 5 mM Mg2(+)-, Ca2(+)-, Mn2(+)- or Co2(+)-containing media exhibited a markedly lower rate of Na(+)-stimulated L-alanine transport. Divalent cation inhibition of L-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 L-alanine transport. Conversely, pretreatment of the vesicles with 0.2 mM of either EGTA or EDTA resulted in higher initial rates of L-alanine transport. This stimulation was overcome by addition of excess divalent cation to the vesicle suspension solution. Since these blLPM vesicles are primarily oriented right-side-out, the divalent cation inhibition of L-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 L-alanine transport across the liver cell plasma membrane.

PubMed ID: 2110482

MeSH Terms: Alanine/metabolism*; Animals; Biological Transport/drug effects; Calcium/pharmacology; Cell Membrane/metabolism; Dose-Response Relationship, Drug; Edetic Acid/pharmacology; Egtazic Acid/pharmacology; Liver/metabolism*; Magnesium/pharmacology; Manganese/pharmacology; Rats; Sodium/metabolism*; Time Factors