High Phosphate Uptake

Human red blood cells reach an equilibrium of phosphate distribution at 37 ° much faster with o . I I M or intermediate levels than with o.o2 M and lower phosphate levels. Other divalent anions added to 0.o2 M phosphate solutions have an action similar to that of the extra phosphate. A past observation that phosphate escapes from red cells more slowly than it enters them appears to have arisen from differences in the phosphate levels to which the cell membrane was exposed. The effect of o . i i M phosphate at 37 ° undergoes reversal when the temperature is lowered to 22 ° , and when the phosphate level is also lowered to 0.02 M. These properties of the red blood cell introduce difficulties in applying tests for mediation in the entry and exit of phosphate. The retarding action of estradiol disulfate, stilbestrol disulfate and stilbestrol on phosphate entry extends from 0.002 to o . I I M phosphate, and applies also to the exodus of phosphate.