Limited and selective localization of the lysosomal membrane glycoproteinsLGP85 and LGP96 in rat osteoclasts

Monospecific antibodies against two major glycoproteins of rat lysosomal me mbranes with apparent molecular masses of 96 and 85 kDa, termed LGP96 and L GP85, respectively, were used as probes to determine the expression and dis tribution of lysosomal membranes in rat osteoclasts. At the light microscop ic level, the preferential immunoreactivity for both proteins was found at high levels at the side facing bone of actively bone-resorbing osteoclasts. Osteoclasts detached from bone surface were devoid of immunoreactivity for each protein. At the electron microscopic level, both proteins were exclus ively confined to the apical plasma membrane at the ruffled border of activ e osteoclasts with well-developed ruffled border membrane. No immunolabelin g for both proteins was observed in the basolateral membrane and the clear zone of bone-resorbing osteoclasts. The plasma membrane of preosteoclasts a nd post-and/or resting osteoclasts showed little or no reactivity against t hese two antibodies. The results indicate that lysosomal membrane glycoprot eins are actively synthesized in active osteoclasts, rapidly transported to the ruffled border area, and contribute to the formation and maintenance o f the acidic resorption lacuna of osteoclasts.