Differences in myofilament calcium sensitivity in rat psoas fibers reconstituted with troponin T isoforms containing the alpha- and beta-exons.
The carboxy terminus of fast skeletal muscle troponin T (fsTnT) is highly conserved. However, mutually exclusive splicing of exons 16 and 17 in the fsTnT gene results in the expression of either the alpha- or beta-fsTnT isoform. The alpha-isoform is expressed only in adult fast skeletal muscle, whereas the beta-isoform is expressed in varying quantities throughout muscle development. Reconstitution of detergent-skinned adult rat psoas muscle fibers with rat fast skeletal troponin complexes containing either fsTnT isoform demonstrated that reconstitution with alpha-fsTnT resulted in greater myofilament Ca(2+) sensitivity than reconstitution with beta-fsTnT, without changes to Ca(2+)-activated maximal tension, ATPase activity or tension cost. The observed isoform-specific differences in myofilament Ca(2+) sensitivity may be due to changes in the transition of the thin-filament regulatory unit from the off to the on state, possibly due to altered interactions of the C-terminus of fsTnT with troponins I and/or C.
Gallon
Clare E
CE
Department of Veterinary Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA 99164-6520, USA.
Tschirgi
Matthew L
ML
Chandra
Murali
M
D008841:Actin Cytoskeleton / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005091:Exons; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D020033:Protein Isoforms / Q000378:metabolism; D016658:Psoas Muscles / Q000502:physiology*; D051381:Rats; D012680:Sensitivity and Specificity; D013329:Structure-Activity Relationship; D020107:Troponin T / Q000235:genetics / Q000378:metabolism*
D020033:Protein Isoforms; D020107:Troponin T; D002118:Calcium