FLUORESCENT RECOVERY AFTER PHOTOBLEACHING (FRAP) OF A FLUORESCENT TRANSFERRIN INTERNALIZED IN THE LATE TRANSFERRIN ENDOCYTIC COMPARTMENT OFLIVING A431 CELLS - THEORY
P. Wahl et F. Azizi, FLUORESCENT RECOVERY AFTER PHOTOBLEACHING (FRAP) OF A FLUORESCENT TRANSFERRIN INTERNALIZED IN THE LATE TRANSFERRIN ENDOCYTIC COMPARTMENT OFLIVING A431 CELLS - THEORY, Biochimica et biophysica acta. Biomembranes, 1327(1), 1997, pp. 69-74
In previous works, other authors characterized a compartment (LCT) of
A431 carcinoma cells in which markers of transferrin endocytose had ac
cumulated during a long chase period. This compartment, was essentiall
y formed by large stationary vacuoles. A few small vesicles budded fro
m these vacuoles, rapidly saltated along microtubules and eventually f
used with other vacuoles, causing an intracellular transport of the ma
rker bound to the limiting membrane (M. De Brabander, R. Nuygens, H. G
eerts, C.R. Hopkins, Cell. Mot. Cytoskel. 9 (1988) 30). In the present
paper, we derived the fluorescence recovery after photobleaching (FRA
P) of a fluorescent marker of LCT. We assumed that the rate of the int
racellular transport of the marker was controlled by the fission-fusio
n process between vesicles and vacuoles. We showed that the concentrat
ion of a bleached fluorescent marker was a decreasing exponential func
tion of the time elapsed from the beginning of the recovery phase. The
rate constant of this exponential was equal to the product of the ves
icle surface by the number of vesicles which fused with a unit of vacu
ole surface during one second. If a fraction of the marker spontaneous
ly reactivated itself with a much higher rate constant of reaction tha
n the rate constant of the transport process, the fractional FRAP of t
he marker was the sum of the fractional FRAP of both processes occurri
ng separately. In a companion paper (F. Azizi, P. Wahl, Biochim. Bioph
ys. Acta 1327 (1997) 75-88), our FRAP experiments will be described an
d analysed with the mathematical expressions derived in the present pa
per. (C) 1997 Elsevier Science B.V.