Modulation of Na+/alanine cotransport in liver sinusoidal membrane vesicles by internal divalent cations.
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.
Simmons
T W
TW
Department of Biophysics, University of Rochester School of Medicine, NY 14642.
Moseley
R H
RH
Boyer
J L
JL
Ballatori
N
N
D000409:Alanine / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D008099:Liver / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
D008345:Manganese; D004533:Egtazic Acid; D004492:Edetic Acid; D012964:Sodium; D008274:Magnesium; D000409:Alanine; D002118:Calcium