Fluorescence imaging of the propagation of excitability in
gastrointestinal muscles
Nelson G. Publicover, Terence K. Smith, and Randel J. Stevens
Program in Biomedical Engineering, MS 400
Department of Physiology and Cell Biology
University of Nevada, Reno NV 89557
Proc. SPIE Vol. 3600, p. 42-50, Biomedical Imaging: Reporters, Dyes,
and Instrumentation, Darryl J. Bornhop; Christopher H. Contag; Eva M. Sevick-Muraca;
Eds.
Publication Date: 07/1999
Abstract:
Fluorescence imaging is a useful tool to study the sequence and dynamics
of the spread of excitability in biological tissues. Gastrointestinal muscles
are particularly amenable to imaging using standard video rates (30 frames/sec)
because the frequency of events is low (1-20 per min) and propagation velocities
are slow (8 cm/sec parallel and 1 cm/sec transverse to the long axis of
muscle fibers). Calcium-sensitive fluorescent indicators such as fluo-3
provide effective markers of excitability because optically they exhibit
high quantum yields and calcium plays important biological roles including
regulating intracellular signaling and muscle contraction. Video sequences
of gastrointestinal tissues demonstrate the existence of multiple preferred
locations to initiate excitability (pacemaker sites). The spatial and temporal
resolution of microscope-based imaging systems allows pacing sites to be
identified within single muscle bundles. Anisotropic conduction velocities
result in spatially complex patterns of excitability where the range of
propagation appears to be limited by "collisions" with neighboring excitable
events or recently activated regions. Although standard video rates are
generally not sufficient to monitor more rapid excitable events such as
nerve action potentials, fluorescence imaging can be used to investigate
excitability mechanisms in tissues such as smooth muscles where event frequencies
and propagation velocities are low.
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