Chen, Gaoping Carroll, Stefanie Racay, Peter Dick, Jim Pette, Dirk Traub, Irmtrud Vrbova, Gerta Eggli, Peter Celio, Marco Schwaller, Beat <jats:p> The soluble Ca<jats:sup>2+</jats:sup>-binding protein parvalbumin (PV) is expressed at high levels in fast-twitch muscles of mice. Deficiency of PV in knockout mice (PV −/−) slows down the speed of twitch relaxation, while maximum force generated during tetanic contraction is unaltered. We observed that PV-deficient fast-twitch muscles were significantly more resistant to fatigue than were the wild type. Thus components involved in Ca<jats:sup>2+</jats:sup> homeostasis during the contraction-relaxation cycle were analyzed. No upregulation of another cytosolic Ca<jats:sup>2+</jats:sup>-binding protein was found. Mitochondria are thought to play a physiological role during muscle relaxation and were thus analyzed. The fractional volume of mitochondria in the fast-twitch muscle extensor digitorum longus (EDL) was almost doubled in PV −/− mice, and this was reflected in an increase of cytochrome coxidase. A faster removal of intracellular Ca<jats:sup>2+</jats:sup>concentration ([Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>) 200–700 ms after fast-twitch muscle stimulation observed in PV −/− muscles supports the role for mitochondria in late [Ca<jats:sup>2+</jats:sup>]<jats:sub>i</jats:sub>removal. The present results also show a significant increase of the density of capillaries in EDL muscles of PV −/− mice. Thus alterations in the dynamics of Ca<jats:sup>2+</jats:sup> transients detected in fast-twitch muscles of PV −/− mice might be linked to the increase in mitochondria volume and capillary density, which contribute to the greater fatigue resistance of these muscles. </jats:p> application/pdf https://sonar.ch/global/documents/139383 eng info:eu-repo/semantics/altIdentifier/doi/10.1152/ajpcell.2001.281.1.c114 info:eu-repo/semantics/altIdentifier/issn/0363-6143 info:eu-repo/semantics/openAccess American Journal of Physiology-Cell Physiology. - American Physiological Society. - 2001, vol. 281, no. 1, p. C114-C122 Cell Biology Physiology Deficiency in parvalbumin increases fatigue resistance in fast-twitch muscle and upregulates mitochondria http://purl.org/coar/resource_type/c_6501