DIFFERENTIAL-EFFECTS OF GENERAL-ANESTHETICS ON THE QUATERNARY STRUCTURE OF THE CA-ATPASES OF CARDIAC AND SKELETAL SARCOPLASMIC-RETICULUM

The effects of the general anesthetics hexanol, halothane, and diethyl ether on Ca-ATPase activity and on the oligomeric state of the Ca-ATP ase of sarcoplasmic reticulum (SR) from cardiac and skeletal muscle we re investigated, The effects of these general anesthetics on Ca-ATPase activity were similar in cardiac and skeletal SR and were characteriz ed by stimulation of Ca-ATPase activity at lower concentrations of ane sthetics and inhibition at higher concentrations. The distribution of the Ca-ATPase among its oligomeric states was estimated from the time- resolved phosphorescence anisotropy (TPA) decay of SX. in which Ca-ATP ase was covalently labeled with erythrosin isothiocyanate (ERITC) or w ith erythrosin iodoacetamide (ERIA), In contrast, to the similar respo nses of Ca-ATPase activity, there were marked differences in the respo nses to general anesthetics of the TPA decay between cardiac and skele tal SR, In cardiac SR hexanol, halothane, and diethyl ether caused pro nounced increases in the limiting anisotropy at very long times (r(inf inity)), which indicate increases in the fraction of oligomers too lar ge to rotate on the millisecond time scale of the experiments, In skel etal SR: by contrast, there were no significant changes in la in respo nse to the three general anesthetics, This difference between cardiac and skeletal SR in response to general anesthetics is not due to the p resence of phospholamban in cardiac SR, since SR from AT-1 cells, whic h have the SERCA2a isoform of Ca-ATPase, but only trace levels of phos pholamban, have increases in r(infinity) in response to the general an esthetics that resemble those in cardiac SR, Experiments with cardiac SR labeled with ERIA give similar results, showing that the results wi th ERITC are not an artifact of the labeling procedure, Increasing the ionic strength with LiCl diminished the proportion of large immobile oligomers of cardiac Ca-ATPase under control conditions but enhanced t he formation of large oligomers in response to hexanol.