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The contractile state of rabbit papillary muscle in relation to stimulation frequency.
Author(s) -
Edman K A,
Jóhannsson M
Publication year - 1976
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.1976.sp011247
Subject(s) - isometric exercise , stimulation , chemistry , muscle contraction , stimulus (psychology) , steady state (chemistry) , contraction (grammar) , medicine , endocrinology , psychology , psychotherapist
1. The relationship between active force and stimulation frequency (0‐25‐5/sec) was studied at 36‐37 degrees C in isolated papillary muscles of the rabbit. 2. The muscle's force producing capability at a given frequency was determined as the isometric twitch response to a test stimulus that was applied at various times after a priming period. The optimum contractile response was obtained at an interval of 0‐8 sec between the test pulse and the last stimulus of the priming period. 3. The optimum contractile response exceeded the steady‐state twitch amplitude at all stimulation frequencies higher than 1/sec. While the steady‐state twitch resonse declined at frequencies higher than 4/sec, the optimum contractile response was steadily increased as the stimulation frequency was raised. 4. The optimum contractile response was also determined after priming the muscle with a sinusoidal a.c. pulse (field strength, 10 V (r.m.s.)/cm; frequency, 20 c/s; duration, 2‐5 sec). The optimum contractile response obtained after a.c. stimulation was 2‐2 times greater than the maximal steady‐state response. Its absolute value was 67‐3+/‐6‐1 mN/mm2 (mean +/‐S.E. of mean, n = 6). 5. The twitch potentiation produced by priming the muscle at a given frequency decayed exponentially in two phases after optimum contractile response had been attained. The time constants of the two phases, determined after a.c. stimulation, were 2‐6+/‐0‐8 (n = 4) and 92‐0+/‐13‐3 sec (n = 7), respectively. 6. The optimum contractile response determined at various stimulation frequencies was linearly related to the fraction of time during which the cell membrane was depolarized (beyond ‐40 mV) by the action potentials. 7. The results are interpreted in terms of a two‐component model of the metabolism of activator calcium in the excitation‐contraction coupling.