The Uptake of Divalent Manganese Ion by Mature Normal Human Red Blood Cells

Abstract

At physiological pH and concentrations of Mn++ in excess of 5 x 10-4 M, study of the Mn++ ion movement into human red cells is complicated by physicochemical alterations of the ion itself. At concentrations below 5 x 10-4 M, the rate of uptake bears a linear relationship to the Mn++ concentration. The permeability constant for inward movement of Mn++ is 2.87 [plus or minus] 0.13 (S.E.) x 10-9 cm./sec. The rate is not influenced by the addition of metabolic substrates such as glucose or adenosine or the metabolic inhibitors iodoacetate or fluoride. Co++, Ca++, and Mg++ do not appear to compete with Mn++ for entry, but at high concentrations relative to Mn++, they reduce the rate of entry. Ca++ is far more effective than Co++ or Mg++ in this regard. The permeability constant for outward Mn++ movement is 1.38 [plus or minus] 0.21 (S.E.) X 10-9 cm./sec., about half of that for entry. This slower rate of outward movement is consistent with the finding that 40 to 60% of the Mn++ taken up by the red cells is non-ultrafilterable. Less than 5 to 10% of the Mn++ appears to be bound to the stroma. It is concluded that entry and exit of Mn++ is a process of passive diffusion involving no carriers, transport, or metabolic linkage.