Iron-transport characteristics of vesicles of brush-border and basolateral plasma membrane from the rat enterocyte

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Abstract
Vesicles of brush-border and basolateral plasma membrane were prepared from enterocytes of the rat small intestine. The separateness of these 2 varieties of plasma membrane was confirmed by appropriate enzyme assays. The uptake of Fe2+ by these membrane vesicles was studied, and differences between the 2 types of membrane in both the amount of Fe2+ taken up and in the rate of uptake were suggested. At low (up to 3 .mu.M) concentrations of Fe2+, uptake by both membrane types showed evidence of saturation and could be blocked with the thiol inactivator N-ethylmaleimide. Fe2+ is apparently taken into an osmotically active space by a process of facilitated diffusion at low concentrations, but at higher concentrations the process appeared to obey 1st-order kinetics. Evidence for the existence of functional polarity in the epithelial cell of the small intestine was provided.