Mammalian tissues express both cation-dependent (CD-MPR) and cation-independent (CI-MPR) mannose-6-phosphate receptors, which mediate the targeting of acid hydrolases to lysosomes. The coexistence of the two receptors in all cell types and tissues is still poorly understood. To determine whether these receptors might play a role in maturation. we studied their expression and binding properties in rat liver during perinatal development. CI-MPR expression decreases progressively from 18-day fetuses to adults, whereas the CD-MPR showed a transient decrease in newborn and at the 5th day after birth. Immunostaining of the tissues showed that both receptors localize to hepatocytes at all the ages and. additionally. the CD-MPR as reactive in megakaryoctes at early stages. Binding assays showed differences in the B-max and K-D values between the piles Studied. These results demonstrate that both receptors change differentially during perinatal development. suggesting that they play distinct roles during organ Maturation. (C) 2002 Elsevier Science (USA). All rights reserved.