Table II.

Quantitative Analysis of Tf-HRP and BSA-Gold Uptake in A20.A^b Cells

A20		Type 1		Type 2		Type 3		Type 4		Type 5/6
3 min		74		21		5		−		−
Tf-HRP
10 min		82		12		6		−		−
Tf-HRP
3 min		63		21		16		−		−
BSA-gold
10 min		55		21		6		8		10
BSA-gold
10 + 20 min		14		3		38		38		7
BSA-gold
10 + 50 min		6		2		10		27		56
BSA-gold

Experiments were performed as described in Table I. Only five types, compared to six types in 6H5.DM cells, showed morphologically distinguishable endocytic compartments in A20.A^b cells. The quantitation of gold particles for Tf-HRP in A20.A^b cells shows the abundant presence of Tf-HRP in type 1 compartments and lower amounts in types 2 and 3. After 3 min of BSA-gold uptake, the tracer is most prominently present in type 1, to some extent in type 2 and 3, but not in type 4 and 5/6 compartments. Already after 10 min of internalization, type 4 and 5/6 compartments contain significant amounts of BSA-gold, and these BSA-gold numbers increase after 20- and 50-min chase.