Abstract
Intracellular calcium regulates numerous cell functions, including amino acid uptake by rat diaphragm and hepatocytes (Arch Biochem 23:96; Proc Nat Acad Sci 77:5953). Therefore, we studied the effect of calcium (Ca) on the uptake of α−amino isobutyric acid (AIB) by human placental slices. During 45 minutes preincubation, tissue calcium was maintained (CaM), or was depleted (CaD) by 2.0 mM EGTA in Ca-free medium. Tissues were then incubated with 125 uM 14C-AIB for 60 minutes in medium with (+) or without (−) Ca. AIB uptake, expressed as the ratio of intracellular to extracellular AIB concentrations (Ci/Co), was 3 53 ± 0.13 (mean ± SE) in controls (CaM+), but was markedly reduced in CaD slices incubated without Ca repletion (CaD−): Ci/Co = 1.66 − 0.08 (p<0.001). Ca repletion during incubation (CaD+) resulted in partial restoration of 60 min AIB uptake: Ci/Co = 2.64 ± 0.11 (p<0.01, compared to either CaM+ or CaD−). In time-course experiments, the slope of AIB uptake for CaD+ was parallel to CaM+ by 15 minutes and linear through 60 minutes. However, CaD− showed no AIB uptake after 30 minutes. Finally, 10 uM verapamil, a calcium channel blocker, reduced 60 minute AIB uptake by 17.5% (p<0.05). CONCLUSION: Calcium regulates human placental uptake of the actively transported, neutral amino acid, AIB. SPECULATION: The placenta may serve as a model for studying calcium regulated amino acid transport in human tissue.
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