title: Quantitative analysis of intramembranous particles in the membranous system of rat liver cells at different stages of development and aging.
abstract: The density of intramembranous protein particles was studied by freeze-fracture. Particle density on the fracture faces of the plasmalemma and the rough endoplasmic reticulum (RER), as well as the outer and inner membranes of the nucleus and the mitochondria in rat hepatocytes were quantified. Comparison among different age groups sampled days postcoitum (dpc), days postpartum (dpp), and months postpartum (mpp) showed age-related changes in particle density in each membrane system. With the exception of the RER, particle densities increased after the 16th dpc, reached a maximum at birth, and then decreased with increasing age. Simultaneously, the number of nuclear pores shows a positive correlation with the particle density of the nuclear membranes. The particle density on the membranes of the RER shows a maximum on the 16th dpc and on the 6th dpp. Thereafter, the density of the RER decreases slightly. In all membrane systems, the density of the particles on the external fracture faces is more variable than density of the particles on the protoplasmic fracture faces.
mesh_terms: D000375:Aging; D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D002467:Cell Nucleus / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000648:ultrastructure; D005614:Freeze Fracturing; D008099:Liver / Q000166:cytology* / Q000254:growth & development / Q000502:physiology; D008297:Male; D008930:Mitochondria, Liver / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains