Permeability of Phospholipid Membranes to Inorganic Phosphate

Abstract

(1) Diffusion of inorganic phosphate through a model phospholipid membrane exhibits an initial time lag but is linear with time thereafter.(2) In 0.1 M NaCl the permeability coefficient k = 3.4 (± 0.14) × 10−8 cm/s and is invariant with Δc, the concentration difference of phosphate across the membrane. The diffusion lag time is 51 ± 20 min.(3) In 0.5 mM MgCl2 the permeability coefficient decreases exponentially as Δc is increased and is less than 10−8 cm/s. The diffusion lag time is 94 ± 38 min.(4) In 0.5 mM MgCl2 the activation energy for phosphate diffusion through the membrane is 20 kcal/mol.(5) The flux of inorganic phosphate through the model membrane is in good agreement with experimental values obtained on erythrocytes.