Amiloride-inhibited Na+-H+ exchange in human kidney medulla microsomes

Membrane vesicles from the medulla of the human kidney are capable of amiloride-inhibited sodium-proton exchange. Sodium uptake into the vesicles is stimulated by low intravesicular pH (6.0) and inhibited by both low extravesicular pH (6.0) and amiloride (2 mM). Sodium uptake is a linear function of the vesicular protein concentration and can be reversed by raising the osmotic strength of the solution to shrink the vesicles or by adding the ionophore nigericin. Acridine orange was accumulated by the vesicles in response to a pH gradient (pH 6.0, inside, 8.0 outside), and the accumulation of acridine orange could be reduced by increased extravesicular sodium. Thus sodium could stimulate proton movement just as protons could stimulate sodium movement across the vesicular membrane.