THE EFFECTS OF HALOTHANE, ENFLURANE, AND ISOFLURANE ON THE LENGTH TENSION RELATION OF THE ISOLATED VENTRICULAR PAPILLARY-MUSCLE OF THE FERRET

The effects of halothane, enflurane, and isoflurance on the length-tension relation were investigated in papillary muscles of the right ventricle of adult male ferrets at 30-degrees-C. Isometric twitch contractions were obtained at lengths ranging from the shortest length yielding the greatest active force development under isometric conditions (L(max)) to 86% of L(max), in two consecutive protocols: first in [Ca2+]o ranging from 0.45 to 2.25 mM, and then in [Ca2+]o 2.25 mM before, during, and after exposure to incremental concentrations of halothane (n = 9 muscles), enflurane (n = 9 muscles), and isoflurane (n 9 muscles), each in steps of 0.25 MAC to total concentrations up to and including 1.5 MAC. Each of the three anesthetics caused a concentration-dependent decrease in developed force. The relative extent of the negative inotropic effect was not different at various muscle lengths. Because myofibrillar Ca2+ responsiveness (Ca2+-affinity of troponin C) decreases at shorter muscle lengths, the results suggest that an alteration in myofibrillar Ca2+ responsiveness by volatile anesthetics is minor relative to the anesthetic-induced decreased intracellular Ca2+ availability in ventricular myocardium.