Fluorescence imaging of the propagation of excitability in gastrointestinal muscles

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.