H. Kutchai et al., DIFFERENTIAL-EFFECTS OF GENERAL-ANESTHETICS ON THE QUATERNARY STRUCTURE OF THE CA-ATPASES OF CARDIAC AND SKELETAL SARCOPLASMIC-RETICULUM, Biochemistry, 37(8), 1998, pp. 2410-2421
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.