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Velocity of sarcomere shortening in rat cardiac muscle: relationship to force, sarcomere length, calcium and time.
Author(s) -
Daniels M,
Noble M I,
ter Keurs H E,
Wohlfart B
Publication year - 1984
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.1984.sp015424
Subject(s) - sarcomere , isometric exercise , chemistry , ventricle , anatomy , cardiac muscle , myocyte , medicine
The relation between force and velocity was determined in sixteen trabeculae of rat right ventricle as a function of time during a twitch, of sarcomere length and of external Ca2+ concentration, [Ca2+]o. The trabeculae were studied in modified Krebs‐Henseleit solution at 25 degrees C. Force was measured with a semiconductor strain gauge. Sarcomere length was measured with a laser diffraction system. A servomotor system was used in which control could be switched between sarcomere length, muscle length and force. Force‐velocity relations were derived from load clamps and from contractions in which sarcomere length was initially held constant followed by a quick release and slower release of the sarcomeres at controlled velocity. Force‐velocity relations were fitted by Hill's equation (Hill, 1938), (Po‐P) b = (P+a) V, where P = force, V = velocity, Po = isometric force in mN/mm2 and a and b are constants. For [Ca2+]o = 2.5 mM, with both interventions the values (mean +/‐ S.D.) were: b = 1.00 +/‐ 0.45 micron/s; a = 9.52 +/‐ 5.60 mN/mm2; Vo measured = 13.6 +/‐ 3.0 micron/s; Vo calculated = 13.4 +/‐ 3.4 micron/s; Po measured = 96.5 +/‐ 25.0 mN/mm2; Po calculated = 119.3 +/‐ 34.5 mN/mm2. Vo rose with [Ca2+]o to a maximum at [Ca2+]o = 1.2 mM when Po was about 50% of maximum, while Po rose with [Ca2+]o to a maximum at above 2.5 mM. Vo rose with time during the twitch to a maximum at 25 ms following onset of contraction; Po was then about 50% of the maximum that was obtained at 120 ms. Vo increased with sarcomere length from zero at a sarcomere length of 1.6 micron to a maximum at 1.85 micron. Between 1.85 micron and 2.3 micron, Vo was constant. At 1.85 micron, Po was about 60% of maximum Po. These results are compatible with the hypothesis that Vo is more sensitive than Po to the amount of Ca2+ bound to the contractile proteins, and that Vo reaches a maximal value with an amount of Ca2+ bound to the contractile proteins at which Po has obtained only about 50% of its maximal value.