Biology Reference
In-Depth Information
FIGURE 9.15
Akiharo Kusumi. Courtesy of Akihiro Kusumi
SPT had its beginnings in a 1985 paper by De Brabander et al.
[24]
, but was, and continues
to be primarily advanced by Kusumi and colleagues. In what is now a classic 1993 biophys-
ical Journal paper, Kusumi
[25]
reported on lateral membrane diffusion of the cell
cell recog-
nition, adhesion receptor E-cadherin in cultured mouse karatinocytes. The paper compared
SPT to the then more established technique of FRAP. Receptor movement was observed by
SPTafter E-cadherin was bound to an anti-cadherin monoclonal antibody coupled to a 40 nm
gold particle. Motion was followed by video-enhanced differential interference contrast
microscopy at a temporal resolution of 30 ms and at a nanometer special precision. After plot-
ting the results as mean square displacement of the gold particle against time, four character-
istic types of motion were observed (
Figure 9.16
):
A.
e
10
12
cm
2
/sec (6%).
Stationary mode where diffusion is less than 4.6
B.
Simple Brownian diffusion mode (28%).
C.
Directed diffusion mode indicated by unidirectional motion (2%).
10
9
cm
2
/s and diffusion is confined within a limited area by the cytoskeleton network (64%).
Diffusion was confined into many small domains 300
10
12
and 1
D.
Confined diffusion mode where Brownian diffusion is between 4.6
600 nm in diameter.
e
Confined Diffusion represented almost two-thirds of the total diffusion patterns. Later
Kusumi noticed that in rat kidney cells, diffusion appeared to be a connected series of
confined diffusion mode domains. In other words the overall, low resolution diffusion
measured by FRAP was composed of two parts, fast Brownian motion that is confined
within corrals and slow 'hop diffusion' that connects the confined zones. Unfortunately,
these observations could not be confirmed in erythrocytes or other cells. Kusumi realized
that a faster methodology was needed. He obtained ultrafast filming technology from
the field of explosives research
[22]
. This technology employed a camera that obtained
40,000 frames per second with a temporal resolution of 25
s. This produced a 1,000
times faster resolution than before (30 ms for the E-cadherin experiment), allowing
Kusumi to even measure hop diffusion for membrane lipids which hop at very fast rates
(
Figure 9.17
).
m
