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An internal viscous element limits unloaded velocity of sarcomere shortening in rat myocardium.
Author(s) -
de Tombe P P,
ter Keurs H E
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019283
Subject(s) - sarcomere , anatomy , ventricle , chemistry , strain (injury) , materials science , biophysics , myocyte , biology , medicine , endocrinology
1. Peak twitch force (F0) and sarcomere length (SL) were measured in trabeculae that had been dissected from the right ventricle of rat heart and that were superfused with a modified Krebs‐Henseleit solution at 25 degrees C. Sarcomere length was measured by laser diffraction techniques. Force was measured with a silicone strain gauge. Unloaded velocity of sarcomere shortening (V0) was measured by the ‘isovelocity release’ technique. 2. At [Ca2+]o = 1.5 mM and SL below 1.9 microns, V0 increased in proportion to SL, while V0 was independent of SL above 1.9 microns. At [Ca2+]o = 0.5 mM, V0 was proportional to SL up to 2.2 microns. At [Ca2+]o = 0.2 mM, V0 was proportional to SL up to 2.3 microns which is the longest SL that we were able to study in our trabeculae. 3. A unique relationship was observed between V0 and F0, irrespective of whether F0 was altered by variation of [Ca2+]o or sarcomere length above slack length. 4. Passive viscosity (Fv) was measured during the pause between contractions in the presence of 1.5 mM [Ca2+bdo and in the range SL = 2.0‐2.1 microns by applying 0.1 micron stretches at various velocities up to v = 30 microns s‐1. The force response to stretch, corrected for the contribution of parallel elastic force, showed viscoelastic characteristics with an exponential increase to a maximum (Fv) during stretch and an exponential decline after the end of the stretch. Fv increased, by 0.3%F0 microns‐1 s‐1, in proportion to v < 5 microns s‐1; the increase of Fv was smaller at higher v, suggesting non‐Newtonian viscous properties. 5. The time constant of the increase of force during the stretch decreased (tau rise congruent to 7 ms to tau rise congruent to 4 ms) with increases in v (congruent to 4 microns s‐1 to v congruent to 10 microns s‐1; P = 0.02). The time constant of decay of force at the end of the stretch also decreased with increases in v (tau decay congruent to 8 ms at v congruent to 4 microns s‐1 to tau decay congruent to 3 ms at v congruent to 30 microns s‐1; P < 0.001). Calculated stiffness of the elastic term of the viscoelastic element was independent of v, i.e. 45‐50 N mm‐3.(ABSTRACT TRUNCATED AT 400 WORDS)