Biomedical Engineering Reference
In-Depth Information
8e-8
7e-8
7.14
6e-8
7.28
5e-8
7.41
4e-8
Choroid
Outer retina
Inner retina
Vitreous
3e-8
100
0
100
200
300
400
Distance from choroid, x (m)
FIGURE 10.9 A typical intraretinal proton concentration spatial distribution measured by a double-
barreled pH microelectrode (tip size of
m) in cat retina. The cell voltage was continuously recorded at
20 readings/s and successive ten readings were averaged for plots. The electrode has an average sensitiv-
ity of 48.6
3
µ
5.9 mV/pH from calibration in three Ringer's solutions of known pH (6.0, 7.0, and 8.0 pH) at
37ºC. (Reproduced from [76], with permission from Cambridge University Press.)
understand hyperglycemia-induced changes in the normal intact cat retina [76, 153].
Hyperglycemia induced an acute panretinal acidifi cation of 0.12 pH, which may con-
tribute to the development of diabetic retinal disease [16]. A similar acidifi cation of 0.1
pH in the inner retinal layer was also detected during retinal artery occlusion [181].
A biological circadian clock with a period of 24 h synchronizes biological activities
and behavior in the day/night cycle. Circadian clocks in the vertebrate retina optimize
retinal function by driving rhythms in gene expression, photoreceptor outer segment
membrane turnover, and visual sensitivity [182]. Circadian changes in retinal extracel-
luar pH have been demonstrated in retinas in vivo as well as in vitro [180]. It has been
suggested that circadian clock regulation of retinal pH refl ects circadian regulation of
retinal energy metabolism [76, 183].
The electrodes used in the above studies were double-barreled glass pH sensi-
tive microelectrodes, and the spatial retinal pH profi le was recorded by withdrawing
the microelectrode tip at a rate of 1
m/step across the retina in vivo or
in vitro . In a typical retina pH profi le (Fig. 10.9), measured in cat retina by the micro-
electrode, started from the choroids (Ph
µ
m/s or 100
µ
m). The pH stead-
ily decreased to a minimum value (a maximum [H ] concentration) in the proximal
portion of the outer nuclear layer (pH
7.41, at distance 0
µ
7.14 at
140
µ
m), then increased to
7.28
m) at the vitreous retinal border. The peak [H ] concentration in this
layer indicated that a net production of proton occurred across the avascular outer
retina [76].
(at
310
µ
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