EFFECTS OF HALOTHANE ON THE SARCOPLASMIC-RETICULUM CA2-ARTERIES( STORES AND CONTRACTILE PROTEINS IN RABBIT PULMONARY)

Background. The authors' purpose of this study was to elucidate the me chanisms of direct effects of halothane on the contractile proteins an d Ca2+ release from the sarcoplasmic reticulum Ca2+ stores using isola ted skinned strips (sarcolemma permealized with saponin) from rabbit p ulmonary arteries. Methods: The sarcoplasmic reticular Ca2+ stores wer e examined by immersing the skinned strips sequentially in solutions t o load Ca2+ into and release Ca2+ from the sarcoplasmic reticulum usin g caffeine, inositol 1,4,5-trisphosphate, or halothane. The contractil e proteins were assessed by activating the strips with Ca2+ followed b y administration of halothane (with or without protein kinase C inhibi tors). Tension, fura-2 fluorescence activated by Ca2+ release, and pho sphorylation of myosin light chains were measured. Results: Halothane (0.07-3.00%) increased Ca2+, tension, and phosphorylation of myosin li ght chains in a dose-dependent manner. Halothane decreased accumulatio n of Ca2+ in the sarcoplasmic reticulum and enhanced the caffeine-indu ced tension transients. In strips pretreated with caffeine or inositol 1,4,5-trisphosphate, halothane-induced tension transients were reduce d but Ca2+ was not. In strips activated by 1 mu M Ca2+, halothane (0.5 -3.0%) decreased 20-45% of the activated force at 15 min. Halothane (3 %) transiently increased the force (20%) associated with increases in Ca2+ and phosphorylation of myosin light chains. The increased force w as abolished and the subsequent relaxation was enhanced by the protein kinase C inhibitor bisindolylmaleimide but not by indolocarbazole Go- 6976. Conclusions: In skinned pulmonary arterial strips, halothane, at clinical concentrations, inhibits uptake of Ca2+ by and induces relea se of Ca2+ from intracellular stores possibly shared by caffeine and i nositol 1,4,5-trisphosphate, which are regulated by phosphorylation of myosin light chains. The time-dependent inhibition of the contractile proteins by halothane may be mediated by Ca2+-independent protein kin ase C.