A. Landesberg et al., EFFECT OF CELLULAR INHOMOGENEITY ON CARDIAC TISSUE MECHANICS BASED ONINTRACELLULAR CONTROL MECHANISMS, American journal of physiology. Heart and circulatory physiology, 39(3), 1996, pp. 1101-1114
Our earlier description of the intracellular control (TC) of contracti
on of a single cell, based on coupling calcium kinetics with cross-bri
dge cycling, is extended here to study the performance of a multicellu
lar inhomogeneous tissue common in pathophysiological situations. Inho
mogeneity in calcium affinity or in cross-bridge kinetics is first sim
ulated by analyzing two fiber segments connected as parallel or serial
duplexes. The calculated characteristics of the parallel duplex are t
ested against our experimental data with two parallel nonuniform rat p
apillary 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 su
bendocardial infarction. Theoretical analysis suggests that the IC mec
hanism decreases the extension of cell necrosis by lowering the energy
consumption of the viable cells in the ischemic zone. The study empha
sizes the importance of IC in determining the global and local functio
n of the inhomogeneous myocardium.