Caffeine- or halothane-induced contractures of masseter muscle are similarto those of vastus muscle in normal humans

Background: Skinned fibers from normal human masseter muscle have greater c affeine 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 pati ents) of vastus bundles (caffeine, n=71, halothane, n=63) using the same pr otocol, 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 respect ively 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-re sponse curves were virtually identical. In the halothane group, neither bas eline 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 bu ndles (1997) developed contractures >0.2 g. Conclusion: Contracture responses of intact cut masseter and vastus bundles (non-skinned) do not differ with respect to caffeine and halothane. Respon ses of skinned fibers might demonstrate greater sensitivity under certain c onditions, but they do not reflect those of intact cut bundles.