Prolonged contraction-relaxation cycle of fast-twitch muscles in parvalbumin knockout mice

The calcium-binding protein parvalbumin (PV) occurs at high concentrations in fast-contracting vertebrate muscle fibers. Its putative role in facilita ting the rapid relaxation of mammalian fast-twitch muscle fibers by acting as a temporary buffer for Ca2+ is still controversial. We generated knockou t mice for PV (PV -/-) and compared the Ca2+ transients and the dynamics of contraction of their muscles with those from heterozygous (PV +/-) and wil d-type (WT) mice. in the muscles of PV-deficient mice, the decay of intrace llular Ca2+ concentration ([Ca2+](i)) after 20-ms stimulation was slower co mpared with WT mice and led to a prolongation of the time required to attai n peak twitch tension and to an extension of the half-relaxation time. The integral [Ca2+](i) in muscle fibers of PV -/- mice was higher and consequen tly the force generated during a single twitch was similar to 40% greater t han in PV +/- and WT animals. Acceleration of the contraction-relaxation cy cle of fast-twitch muscle fibers by PV may confer an advantage in the perfo rmance of rapid, phasic movements.