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Force relaxation, labile heat and parvalbumin content of skeletal muscle fibres of Xenopus laevis.
Author(s) -
Lännergren J,
Elzinga G,
Stienen G J
Publication year - 1993
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.1993.sp019587
Subject(s) - chemistry , xenopus , relaxation (psychology) , myofibril , skeletal muscle , stimulation , tetanus , biophysics , nuclear magnetic resonance , anatomy , analytical chemistry (journal) , biochemistry , endocrinology , medicine , chromatography , biology , immunology , physics , gene , vaccination
1. Measurements were made of stable (hb) and labile (ha) maintenance heat rate, slowing of relaxation as a function of tetanus duration, and parvalbumin (PA) content in intact single muscle fibres of types 1 and 2 from Xenopus laevis. The majority of experiments were performed at 20 degrees C. In addition, total and myofibrillar ATPase activity was measured in skinned Xenopus fibres, also of types 1 and 2; these studies were performed at 4 degrees C. 2. In agreement with a previous study hb was significantly higher in type 1 (175 +/‐ 13 mW (g wet wt)‐1; n = 8) than in type 2 fibres (88 +/‐ 9 mW (g wet wt)‐1; n = 7). The value of ha was 236 +/‐ 22 and 117 +/‐ 16 mW (g wet wt)‐1, respectively (mean +/‐ S.E.M.). ha decayed with a time constant of 0.27 +/‐ 0.02 (n = 8) and 0.33 +/‐ 0.02 s (n = 7). 3. The early relaxation rate of tetanic force, extrapolated to the onset of stimulation (yo + yb; where yo is ‘extra’ rate of relaxation and yb steady rate) was 85.6 +/‐ 4.2 s‐1 for type 1 fibres (n = 8) and 62.7 +/‐ 7.3 s‐1 for type 2 fibres (n = 7). Relaxation rate at the end of a 1.8 s tetanus (yb) was 29.4 +/‐ 1.6 and 33.3 +/‐ 1.5 s‐1, respectively; thus, there was more slowing with tetanus duration in type 1 fibres. The time constant for slowing of relaxation with tetanus duration was similar to that for decay of ha. 4. Parvalbumin concentration, [PA], was 0.45 +/‐ 0.04 mM in type 1 (n = 7) and 0.22 +/‐ 0.04 mM (n = 7) in type 2 fibres. 5. For individual fibres positive correlations were found between the ‘extra’ rate of relaxation (yo), labile heat (ha) and [PA]. Significantly more labile heat was liberated than can be accounted for by the enthalpy change of Ca2+ binding to PA. 6. For five fibres (type 1) studied both at 20 and 10 degrees C, the magnitude of slowing of relaxation, expressed as yo/(yo + yb), was 0.58 +/‐ 0.03 at 20 degrees C and 0.65 +/‐ 0.03 at 10 degrees C. 7. Both slowing of relaxation and labile heat were depressed in the second of two closely spaced tetani in type 1 fibres. Repriming of both effects followed similar, biphasic time courses and required more than 10 min for completion at 20 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)