Biology Reference
In-Depth Information
detection was explored based on response times of about 1 s reported for CaSMs
commonly used at that time (
Ammann, 1986
). The general measuring protocol
includes intermittent collection of ion concentration by a single CaSM at a position
near the biological preparation and then at a position some distance away orthog-
onal to the source. A CaSM is shown in
Fig. 2
A and B at the two positions, next to
a mouse pancreatic islet. The excursion distance in this case is 20
m
m but can vary
between 5 and 50
m
m depending on the size of the cell or cellular preparation.
At each pole of excursion, the CaSM is allowed to reach equilibrium (
0.25 s)
before recording the average local ion concentration for about 1 s. Considering
that the CaSMs possess response times of less than 0.1 s, 0.25 s is plenty of time to
reach equilibrium. The CaSM is then immediately positioned to the opposite pole,
and allowed to reach equilibrium before recording the local ion concentration. The
movement of the CaSM between the two positions is controlled by stepper motors
set to move the sensor at a rate of 40
m
m/s such that it takes 0.25 s to reach its new
A
B
Near pole (
E
1
)
Far pole (
E
2
)
50
m
m
C
Δ
E
=
E
1
−
E
2
Near pole
Δ
E
Far pole
d
d
d
d
E
2
E
1
E
2
E
1
Fig. 2
Ca
2
þ
flux measurements performed with self-referencing of a Ca
2
þ
-selective microelectrode
near a mouse pancreatic islet. (A) In the near pole the CaSM collects the average [Ca
2
þ
]-dependent
potential for 1 s, E
1
. (B) After movement to the far pole and equilibration, the average [Ca
2
þ
]-dependent
potential is collected again for 1 s, E
2
. (C) Data collection scheme portraying Ca
2
þ
e
Z
ux. The auto-
mated determination of the di
V
erential [Ca
2
þ
]-dependent potential,
D
E, is used to determine Ca
2
þ
flux.
This measuring scheme continues, as defined by the user. The [Ca
2
þ
]-dependent potential is discarded,
(d), during periods of movement (
0.25 s) and during equilibration in the new position (
0.25 s).
