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Departments of Biomedical Engineering, Surgery, and Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908
In this report we demonstrate electrical
communication in the microcirculation between arterioles and capillary
networks in situ. Microvessel networks in the hamster cheek pouch,
which included capillaries and their feeding arterioles, were labeled
with the voltage-sensitive dye di-8-ANEPPS by intraluminal perfusion
through a micropipette. Pulses of 140 mM potassium solution were
applied by pressure ejection from micropipettes positioned on
arterioles several hundred micrometers upstream from capillaries.
Potassium caused membrane potential changes of 3-11 mV in
capillary segments up to 1,200 µm distal to the stimulation site,
with time delays of <1 s. Capillary membrane potential changes were
biphasic, with initial depolarizations followed by hyperpolarizations.
The size of the response decreased exponentially with the distance
between the arteriole and capillary, with a 1/e distance of 590 µm.
The time to peak depolarization of both arteriolar and capillary
segments was similar. The time to peak response was significantly
faster than that for responses from direct stimulation of capillaries. Capillary responses were also obtained when blood flow was either blocked or directed toward sites of stimulation. Acetylcholine (10
4 M) and phenylephrine
(10
5 M) applied to the
arterioles by iontophoresis produced monophasic hyperpolarizing and
depolarizing responses, respectively, in capillaries with <1-s
delay between stimulus and onset of the membrane potential change.
These results provide evidence in situ of a pathway for electrical
communication between arteriolar and capillary levels of the
microcirculation.
endothelium; membrane potential; voltage-sensitive dye; fluorescence imaging microscopy; ratiometric recording; di-8-ANEPPS
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