Cell partitioning in two-polymer aqueous phase systems and cell electrophoresis in aqueous polymer solutions. Human and rat young and old red blood cells.
It has recently been found that electrophoresis in solutions of appropriately selected polymers in phosphate-buffered saline (PBS) can differentiate between some closely related cell populations which have identical electrophoretic mobilities (EPM) in PBS (e.g., human young and old red blood cells (RBC); RBC from Alzheimer patients and normal individuals). The EPM differences detected in polymer solutions are most likely a consequence of cell- and polymer-specific interactions. Aspects of the relation between the electrophoresis in aqueous polymer solutions of native and in vitro treated young and old RBC (from human and rat) and their partitioning in a charge-sensitive dextran-poly(ethylene glycol) (PEG) aqueous phase system (i.e., a system with a Donnan potential between the phases, top phase positive) have been examined further and are discussed. Unlike the behavior of RBC from Alzheimer patients and normal individuals in which an EPM difference can be detected in PEG solutions but not in dextran, differences in EPM between human young and old RBC are detectable in solutions of either polymer. Selected enzyme treatments of human young and old RBC or their fixation with aldehyde eliminates the EPM differences in dextran; while neuraminidase treatment or formaldehyde fixation of rat young and old RBC retains EPM differences in dextran between these cells. In these latter cases partitioning differences are also in evidence and are in the same direction as the cells' relative EPM (i.e., old RBC < young RBC). The earlier hypothesis that cell partitioning is 'more sensitive' than cell electrophoresis in detecting differences in surface charge between cells bears reexamination because human young and old RBC, which cannot be differentiated by single-tube partitioning in a charge-sensitive phase system, have different EPM in polymer solutions. The difference between these cells can be detected by partitioning but only by use of a multiple-extraction procedure. It is then found to be in a direction similar to the cells' relative EPM in dextran (i.e., human old RBC > young RBC). Rat young and old RBC have different partitions (rat old RBC < young RBC) and different EPM (also rat old RBC < young RBC). Thus, while cell partitioning in a charge-sensitive dextran-PEG aqueous phase system and cell electrophoresis in polymer solution seem to reflect, at least with these cell subpopulations, qualitatively analogous differences in surface properties (in that increasing partitions and EPM are concomitant), there are instances in which either of these physical measurements discerns surface differences which escape detection by the other.