Transport of adenosine by renal brush border membranes

The transport of adenosine into brush border membrane vesicles from rat kidney is demonstrated. A first, rapid stage of transport is completed by 20 s. It is stimulated by a gradient of sodium. The effect of the concentration of adenosine in the low micromolar range on the initial rate of uptake indicates a saturability. An apparent Km of 1.48 microM and a Vmax of 215 pmol/mg protein/min have been calculated. In the rapid stage of uptake, adenosine is transported into the intravesicular space with no significant binding to the membrane. The following slow uptake is not stimulated by sodium and reaches steady state after about one hour.