AJP - Heart and Circulatory Physiology, Vol 270, Issue 3 1101-H1114, Copyright © 1996 by American Physiological Society
Effect of cellular inhomogeneity on cardiac tissue mechanics based on intracellular control mechanisms
A. Landesberg, V. S. Markhasin, R. Beyar and S. Sideman
Julius Silver Institute, Department of Biomedical Engineering, Technion-Israel Institute of Technology, Haifa, Israel.
Our earlier description of the intracellular control (IC) of contraction of
a single cell, based on coupling calcium kinetics with cross-bridge
cycling, is extended here to study the performance of a multicellular
inhomogeneous tissue common in pathophysiological situations. Inhomogeneity
in calcium affinity or in cross-bridge kinetics is first simulated by
analyzing two fiber segments connected as parallel or serial duplexes. The
calculated characteristics of the parallel duplex are tested against our
experimental data with two parallel nonuniform rat papillary fibers. The
predicted serial duplex behavior is compared with reported experimental
data of the effects of segmental hypoxia along a papillary fiber. Fiber
inhomogeneity leads to polyphasic contraction of the fiber segments,
reduces muscle length shortening, and affects the control of relaxation. We
next investigated the force generated by a nonuniform tissue containing
small areas of necrosis, evident in subendocardial infarction. Theoretical
analysis suggests that the IC mechanism decreases the extension of cell
necrosis by lowering the energy consumption of the viable cells in the
ischemic zone. The study emphasizes the importance of IC in determining the
global and local function of the inhomogeneous myocardium.
