Caffeine- or halothane-induced contractures of masseter muscle are similar to those of vastus muscle in normal humans.
BACKGROUND
Skinned fibers from normal human masseter muscle have greater caffeine and calcium sensitivity than skinned fibers from vastus muscle. We examined sensitivity to caffeine and halothane in fresh, cut muscle bundles (non-skinned) from human masseter muscle.


METHODS
Masseter bundles (caffeine, n=25, halothane, n=19) excised from 10 humans under general anesthesia had tension measured in 37 degrees C baths during the addition of caffeine (0.5, 1, 2, 4, 8, 32 mM) or 3% halothane. Results were compared to those of our previous studies (1989, 1997, 25 patients) of vastus bundles (caffeine, n=71, halothane, n=63) using the same protocol, technicians, and equipment.


RESULTS
Baseline force in the caffeine test was 2.10+/-1.57 for masseter, and 2.02+/-1.68 and 1.82+/-1.29 respectively for vastus muscle. Force at 32 mM caffeine concentration was 11.2+/-9.9 g for masseter, 11.0+/-5.4 and 13.5+/-7.5 g for vastus. Concentration-response curves were virtually identical. In the halothane group, neither baseline values (masseter 1.47+/-1.30, vastus 1.91+/-1.32 and 2.15+/-1.71) nor contractures in response to 3% halothane were different. Most bundles had no contracture in response to 3% halothane; 3 masseter bundles and 2 vastus bundles (1989) developed contractures of less than 0.05 g. Three vastus bundles (1997) developed contractures >0.2 g.


CONCLUSIONS
Contracture responses of intact cut masseter and vastus bundles (non-skinned) do not differ with respect to caffeine and halothane. Responses of skinned fibers might demonstrate greater sensitivity under certain conditions, but they do not reflect those of intact cut bundles.
Melton
A T
AT
Department of Anesthesiology, University of California, Davis, USA.
Antognini
J F
JF
Gronert
G A
GA
D000368:Aged; D000369:Aged, 80 and over; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000494:pharmacology*; D003286:Contracture / Q000139:chemically induced*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006221:Halothane / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D008297:Male; D008305:Malignant Hyperthermia / Q000175:diagnosis / Q000503:physiopathology; D008406:Masseter Muscle / Q000187:drug effects*; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects*; D012508:Sarcolemma / Q000187:drug effects
D018685:Anesthetics, Inhalation; D000697:Central Nervous System Stimulants; D002110:Caffeine; D006221:Halothane