Spreading behavior and surface characteristics of young and senescent WI38 fibroblasts revealed by scanning electron microscopy

Abstract

Scanning electron microscopy (SEM) revealed quantitative differences in both surface characteristics and spreading behavior of young and senescent WI38 human diploid fibroblasts. Measurement of spreading behavior involved the determination of the rate of cell elongation beyond an axial ratio of 1.5 after time intervals of 1.5, 3, 6, 9, and 12 h following subculture. Early passage cells exhibited a 44–52% increased spreading rate compared with later passage cells, both obeying zero-order kinetics. Surface microvilli and blebs were also found to vary in number and size after those same time intervals following subculture. In young cells, microvilli density was found initially to be very low but then increased steadily with time. Later passage cells exhibited an initial high density of microvilli, followed by a gradual disappearance with time. The density of cellular blebs did not, however, vary significantly with time following subculture. After approx. 24 h, both early and late passage cells resembled each other. These studies do show that physical membrane characteristics of young and senescent cells differ under certain conditions, and suggest the importance of that structure in the phenomena of senescence.