Table 1. Effects of different inhibitors on internalization of proteins via endocytosis-like mechanisms.

Uptake parameter	Direct penetration	Receptor-mediated endocytosis	Macro- pinocytosis	Inhibitor	Final conc.	Effect on rS3-PA uptake*
Temperature	-	+	+	4°C		No
Energy	-	+	-	Sodium azide	0.1%	No
Interaction with the cell membrane	+	-	+	Soluble heparan sulfates	50 µg/ml	Yes
Caveolin-mediated uptake	-	-	-	Nystatin	25 µg/ml	No
Clathrin-mediated uptake	-	+	-	Brefeldin A	10 µM	No
Actin polymerization	-	-	+	Cytochalasin D	5 µM	No
Endosomal release	-	+	+	Chloroquine (enhancer)	50, 100 µM	No

^*Determined by protein gel blotting.