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Fig. 4. Ca
2+
sparks in isolated cerebral artery myocytes. (
a
) Original images of a Ca
2+
spark recorded every 17 ms from an
isolated cerebral artery myocyte.
White scale bar
represents 10
μ
m.
Red arrow
indicates a Ca
2+
spark. (
b
)
F
0
image
obtained by averaging 30 consecutive images without a Ca
2+
spark. Trace represents time course of fractional fl uorescence
changes (
F
/
F
0
) during the Ca
2+
spark shown in (
a
) using the analysis area (2.1
μ
m × 2.1
μ
m) depicted as a
red square
in
the
F
0
image.
Gray bar
represents time elapsed during the images shown in (
a
). (
c
)
Pseudo-colored
images of the same
Ca
2+
spark depicted in (
a
) and (
b
). Each pixel is converted to pseudo-color shown in the
color bar
to the right of the images.
White scale bar
represents 10
μ
m .
parameter to describe Ca
2+
spark activity. In isolated myocytes, Ca
2+
spark frequency, expressed in Hz, represents the total number of
events occurring in a cell divided by the sampling period (s). In
cerebral artery myocytes, Ca
2+
spark frequency is increased by vaso-
dilators acting via increased cyclic AMP-dependent protein kinase,
cyclic GMP-dependent protein kinase and/or increased levels of
cytosolic or SR Ca
2+
(
6, 10, 11
). Conversely, enhanced cerebral
artery constriction following SAH is associated with a reduction in
Ca
2+
spark frequency in cerebral artery myocytes (
13, 15
). Ca
2+
spark amplitude is frequently expressed as the maximum fractional
fl uorescence (
F
/
F
0
) increase (Fig.
5c
). Using Ca
2+
spark-induced
large conductance Ca
2+
-activated K
+
(BK) channel activity as a bio-
logical Ca
2+
indicator, Perez et al. (
7
) have estimated that local
increases in Ca
2+
during a Ca
2+
spark are in the range of 4-30
μ
M.
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