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

Abstract

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. 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. 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. In FDB, the effects of tetanus duration on WT and PVKO muscles were qualitatively similar to those observed in EDL. 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. 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. 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).

Somatic calcium level reports integrated spiking activity of cerebellar interneurons in vitro and in vivo

“…These properties are well studied for PV (for reviews, see Schwaller 2009Schwaller , 2010 source was studied in a murine PV-expressing fast-twitch muscle subjected to tetanic stimulation. It was found that in wild-type muscles the relaxation rate depends on tetanus duration, whereas this does not occur in muscles from PVϪ/Ϫ mice (Raymackers et al 2000). Thus the fraction of Ca 2ϩ -bound PV resulting from an increase in tetanic stimulation determines the relaxation rate.…”

Cytosolic Ca2+ Buffers

“…An often-neglected aspect is the role of Ca 2þ buffers in acting as transient Ca 2þ sources, prolonging the [Ca 2þ ] i decay. In fast-twitch muscles subjected to long tetanic contractions, PV saturates with Ca 2þ and consequently slows down relaxation (Raymackers et al 2000). The slow decay component mediated by Ca 2þ -bound PV also leads to a robust, PV-dependent, delayed transmitter release at cerebellar interneuron -interneuron synapses subsequent to presynaptic bursts of action potentials (Collin et al 2005).…”

Parvalbumin correlates with relaxation rate in the swimming muscle of sheepshead and kingfish

“…However, this has not been tested. Prolonged muscle stimulation leads to saturation of the available parvalbumin, diminishing its contribution to relaxation (Hou et al, 1991;Raymackers et al, 2000). Dissociation rates for Ca 2+ determine how quickly parvalbumin is able to recover from saturation (Hou et al, 1991).…”