Uptake of ?-aminoisobutyric acid and phosphate by membrane vesicles derived from growing and quiescent fibroblasts

Abstract

Membrane vesicles derived principally from the plasma membrane and endoplasmic reticulum of mouse 3T3 cells transformed by Simian virus 40 take up α‐aminoisobutyric acid (AIB) and phosphate (Pi). When NaCl is added simultaneously with AIB or Pi, uptake rises two‐ to three‐times above the equilibrium uptake value found in the absence of NaCl. The ability to accumulate AIB or Pi over the control value, in the presence of a Na⁺ gradient, is almost lost in membrane vesicles derived from benzpyrene‐transformed 3T3 cells (BP3T3) arrested in the G₁ phase of the cell cycle by serum starvation. When added to the membranes with NaCl and the uptake substrate, a combination of fibroblast growth factor (FGF) and epidermal growth factor (EGF) restores the ability of the membranes to accumulate AIB and Pi over the control value.