Surface charge of macrophages and their interaction with charged particles

The distribution and concentration of surface ionogenic groups on murine peritoneal macrophages and the responses of their plasmalemma to charged markers were investigated by electron microscopy. Quantitation of the distribution of cationized ferritin (CF) as a marker for anionic groups on fixed cells revealed surface anions on invaginated parts of the plasmalemma to be fewer than those on flat or projecting segments. Cationic groups on the surface membrane, however, could not be labeled with anionized ferritin (AF). Interaction of viable macrophages with cationic particles at 37 degrees C resulted in their "internalization" within vesicles and coated pits and a closer apposition between many segments of plasmalemma than with neutral or anionic substances. The process occurred unaltered at 4 degrees C and was unaffected by cytochalasin B and colchicine, suggesting that this close apposition between segments of plasmalemma resulted from neutralization of surface negative electrostatic charges by the cationic material and did not reflect endocytosis.