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Myofilament Calcium Sensitivity in Skinned Rat Cardiac Trabeculae

Summary: Myofilament Calcium Sensitivity in Skinned
Rat Cardiac Trabeculae
Role of Interfilament Spacing
John P. Konhilas, Thomas C. Irving, Pieter P. de Tombe
Abstract--The increase in myofilament Ca2
responsiveness on an increase in sarcomere length (SL) is, in part, the cellular
basis for Frank-Starling's law of the heart. It has been suggested that a decrease in myofilament lattice spacing (LS) in
response to an increase in SL underlies this phenomenon. This hypothesis is supported by previous studies in which
reduced muscle width induced by osmotic compression was associated with an increase in Ca2
sensitivity, mimicking
those changes observed with an increase in SL. To evaluate this hypothesis, we directly measured LS by synchrotron
x-ray diffraction as function of SL in skinned rat cardiac trabeculae bathed in 0% to 6% dextran solutions (MW
413 000). We found that EC50, [Ca2
] at which force is half-maximal, at SL between 1.95 and 2.25 m did not vary in
proportion to LS when 3% or 6% dextran solutions were applied. We also found that moderate compression (1%
dextran) of skinned trabeculae at SL 2.02 m reduced LS (LS 42.29 0.14 nm) to match that of uncompressed fibers
at a long SL (SL 2.19 m; LS 42.28 0.15 nm). Whereas increasing SL from 2.02 to 2.19 m significantly increased
sensitivity as indexed by the EC50 parameter (2.87 0.11 mol/L to 2.52 0.12 mol/L), similar reduction in
myofilament lattice spacing achieved by compression with 1% dextran did not alter Ca2


Source: Akabas, Myles - Department of Physiology and Biophysics, Albert Einstein College of Medicine, Yeshiva University


Collections: Biology and Medicine