In vitro human masseter muscle hypersensitivity: a possible
explanation for increase in masseter tone.
Adnet, Pascal J., Hugo Reyford, Benoit M. Tavernier, Toussaint
Etchrivi, Ivan Krivosic, R. Krivosic-Horber, and Ghislain Haudecoeur.
Departments of Anesthesiology, Pharmacology, and Neuropathology,
Unit[acute]e de Recherche sur l'Hyperthermie Maligne, (Groupe
C.I.V.I.S), H[circumflex]opital B, Centre Hospitalier et
Universitaire de Lille, 59037 Lille C[acute]edex, France
APStracts 3:0011A, 1996.
To determine whether a difference in fiber-type caffeine and calcium
(Ca++) sensitivities exist 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 more than 10 % of the maximal
tension obtained after loading the fiber with a calcium 1.6 x 10-2 mM
solution for 30 seconds. Significant difference in the mean (+ SD)
caffeine sensitivity was found between type I masseter fibers (2.57 +
1.32 mM) versus type I (6.02 + 1.74 mM) and type II vastus lateralis
fibers (11.25 + 3.13 mM). Maximal Ca++-activated force per cross
-sectional area was significantly different between masseter and
vastus lateralis fibers. However, the Ca++ 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.
Received 2 February 1995; accepted in final form 11 December
1995.
APS Manuscript Number A126-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96