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Fig. 2. Simultaneous measurement of global [Ca
2+
]
i
and diameter of an intact pressurized cerebral artery. Fluorescence
intensity (photomultiplier tube counts) at 340 and 380 nm excitation (
F
340 and
F
380, respectively),
F
340/
F
380 ratio, cal-
culated free [Ca
2+
]
i
and arterial diameter from a pressurized rabbit cerebellar artery. Smooth muscle membrane potential
depolarization induced by elevating extracellular K
+
from 3 to 60 mM caused an increase in
F
340/
F
380 ratio (i.e. increased
free [Ca
2+
]
i
) and vasoconstriction. The response to 60 mM K
+
was reversed by application of the VDCC blocker nifedipine
(1
μ
M ) .
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