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 isoflurane 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 (Lmax) to 86% of Lmax, 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.