title: Effects of volatile anesthetics on directly and indirectly stimulated skeletal muscle.
abstract: Isolated guinea pig nerve-lumbrical muscle preparations were exposed to halothane, methoxyflurane, isoflurane, enflurane, fluroxene, and diethyl ether. The temporal courses of the effects on indirectly and directly elicited twitch responses were determined over a range of concentrations for each agent. When the anesthetics were compared at concentrations equivalent in terms of minimum alveolar concentration (MAC), a spectrum was observed in which halothane, methoxyflurane and isoflurane depressed the indirect twitch response at 3.5--5 MAC and the direct twitch response at 8--10 MAC. Diethyl ether and fluroxene depressed the indirect twitch response at 2--3.5 MAC and the direct twitch response at 3--6 MAC. Enflurane depressed the indirect response at 1.5--2.5 MAC and the direct response at 6--8 MAC. When the anesthetics were compared at concentrations equivalent in terms of their abilities to depress end-plate depolarization, however, all anesthetics were equipotent. Depression of the indirect twitch response occurred only when anesthetic concentrations were great enough to depress depolarization by 50 per cent.
mesh_terms: D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D004558:Electric Stimulation; D004737:Enflurane / Q000494:pharmacology; D004986:Ether / Q000494:pharmacology; D004987:Ethers / Q000494:pharmacology; D006168:Guinea Pigs; D006221:Halothane / Q000494:pharmacology; D066298:In Vitro Techniques; D007530:Isoflurane / Q000494:pharmacology; D008733:Methoxyflurane / Q000494:pharmacology; D009045:Motor Endplate / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects* / Q000294:innervation; D010525:Peripheral Nerves / Q000187:drug effects; D013268:Stimulation, Chemical
chemical_list: D000777:Anesthetics; D004987:Ethers; D004986:Ether; D008733:Methoxyflurane; D004737:Enflurane; D007530:Isoflurane; D006221:Halothane