Tetanus relaxation of fast skeletal muscles of the mouse made parvalbumin deficient by gene inactivation

Open Access
Publisher Website
Google Scholar
Abstract
1 The effects of tetanus duration on the relaxation rate of extensor digitorum longus (EDL) and flexor digitorum brevis (FDB) muscles were studied in normal (wild-type, WT) and parvalbumin-deficient (PVKO) mice, at 20 °C. 2 In EDL of PVKO, the relaxation rate was low and unaffected by tetanus duration (< 3.2 s). In contrast, the relaxation rate of WT muscles decreased when tetanus duration increased from 0.2 to 3.2 s. In WT muscles, fast relaxation recovered as the rest interval increased. 3 Specific effect of parvalbumin was asserted by calculating the difference in relaxation rate between WT and PVKO muscles. For EDL, the rate constant of relaxation slowing was 1.10 s−1 of tetanization; the rate constant of relaxation recovery was 0.05 s−1 of rest. 4 In FDB, the effects of tetanus duration on WT and PVKO muscles were qualitatively similar to those observed in EDL. 5 Relaxation slowing as tetanus duration increases, reflects the progressive saturation of parvalbumin by Ca2+, while recovery as rest interval increases reflects the return to Ca2+-free parvalbumin. 6 At all tetanus durations, relaxation rate still remained slightly faster in WT muscles. This suggested that parvalbumin facilitates calcium traffic from myofibrils to the SR. 7 No difference was found between WT and PVKO muscles for: (i) the expression of the fast isoforms of myosin heavy chains, (ii) the force-velocity relationship and maximal shortening velocity and (iii) the Ca2+-activated ATPase activity from isolated preparations of the sarcoplasmic reticulum (SR).