title: In vitro human masseter muscle hypersensitivity: a possible explanation for increase in masseter tone.
abstract: To determine whether a difference in fiber-type caffeine and Ca2+ sensitivities exists between human masseter and vastus lateralis skeletal muscle, we compared the fiber-type caffeine sensitivities in chemically skinned muscle fibers from 13 masseter and 18 vastus lateralis muscles. Caffeine sensitivity was defined as the threshold concentration inducing > 10% of the maximal tension obtained after the fiber was loaded with a 1.6 x 10(-2) mM Ca2+ solution for 30 s. Significant difference in the mean caffeine sensitivity was found between type I masseter fibers [2.57 +/- 1.32 (SD) mM] vs. type I (6.02 +/- 1.74 mM) and type II vastus lateralis fibers (11.25 +/- 3.13 mM). Maximal Ca(2+)-activated force per cross-sectional area was significantly different between masseter and vastus lateralis fibers. However, the Ca2+ concentration corresponding to half-maximal tension (pCa50) was not significantly different between type I masseter (pCa50 5.9 +/- 0.02) and type I vastus lateralis muscle (pCa50 6.01 +/- 0.08). These results suggest that the increase in caffeine sensitivity of masseter muscle reflects the presence of a low reactivity threshold of the sarcoplasmic reticulum.
authors.affiliation: Department of Anesthesiology, Hôpital B, Centre Hospitalier et Universitaire de Lille, France.
authors.forename: P J
authors.initials: PJ
authors.lastname: Adnet
authors.forename: H
authors.initials: H
authors.lastname: Reyford
authors.forename: B M
authors.initials: BM
authors.lastname: Tavernier
authors.forename: T
authors.initials: T
authors.lastname: Etchrivi
authors.forename: I
authors.initials: I
authors.lastname: Krivosic
authors.forename: R
authors.initials: R
authors.lastname: Krivosic-Horber
authors.forename: G
authors.initials: G
authors.lastname: Haudecoeur
mesh_terms: D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D008406:Masseter Muscle / Q000187:drug effects / Q000502:physiology*; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects*; D012680:Sensitivity and Specificity
chemical_list: D002110:Caffeine; D002118:Calcium