Biophys J, January 2000, p. 164-173, Vol. 78, No. 1

Spatial Ca²⁺ Distribution in Contracting Skeletal and Cardiac Muscle Cells

M. E. Zoghbi,^* P. Bolaños,^* C. Villalba-Galea,^* A. Marcano, E. Hernández, M. Fill, and A. L. Escobar^*

Instituto Venezolano de Investigaciones Científicas,  ^*Centro de Biofísica y Bioquímica,  Centro de Física, Pipe, Venezuela, and  Department of Physiology, Loyola University of Chicago, Maywood, Illinois 60153 USA

The spatiotemporal distribution of intracellular Ca²⁺ release in contracting skeletal and cardiac muscle cells was defined using a snapshot imaging technique. Calcium imaging was performed on intact skeletal and cardiac muscle cells during contractions induced by an action potential (AP). The sarcomere length of the skeletal and cardiac cells was ~2 µm. Imaging Rhod-2 fluorescence only during a very brief (7 ns) snapshot of excitation light minimized potential image-blurring artifacts due to movement and/or diffusion. In skeletal muscle cells, the AP triggered a large fast Ca²⁺ transient that peaked in less than 3 ms. Distinct subsarcomeric Ca²⁺ gradients were evident during the first 4 ms of the skeletal Ca²⁺ transient. In cardiac muscle, the AP-triggered Ca²⁺ transient was much slower and peaked in ~100 ms. In contrast to the skeletal case, there were no detectable subsarcomeric Ca²⁺ gradients during the cardiac Ca²⁺ transient. Theoretical simulations suggest that the subsarcomeric Ca²⁺ gradients seen in skeletal muscle were detectable because of the high speed and synchrony of local Ca²⁺ release. Slower asynchronous recruitment of local Ca²⁺ release units may account for the absence of detectable subsarcomeric Ca²⁺ gradients in cardiac muscle. The speed and synchrony of local Ca²⁺ gradients are quite different in AP-activated contracting cardiac and skeletal muscle cells at normal resting sarcomere lengths.

Biophys J, January 2000, p. 164-173, Vol. 78, No. 1
© 2000 by the Biophysical Society   0006-3495/00/01/164/10  $2.00

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