title: Rabbit skeletal muscle sarcoplasmic reticulum Ca(2+)-ATPase activity: stimulation in vitro by thyroid hormone analogues and bipyridines.
abstract: Sarcoplasmic reticulum-enriched membranes from rabbit skeletal muscle contained Ca(2+)-ATPase activity which was significantly enhanced (26% increase, P < 0.001) in vitro by physiological concentrations (10(-10) M) of L-thyroxine (T4) and 3,3',5-triiodo-L-thyronine (T3). In contrast, the biologically inactive iodothyronine analogues D-T4 and 3,3',5,5'-tetraiodothyroacetic acid (Tetrac) (10(-10) M) were without effect on enzyme activity. 3,5-Dimethyl-3'-isopropyl-L-thyronine (Dimit), a bioactive analogue, was highly effective as a Ca(2+)-ATPase stimulator, increasing enzyme activity by 43% (P < 0.02 vs. T4 effect). A bipyridine cardiac inotropic agent, milrinone, has been reported to be thyromimetic in a myocardial membrane Ca(2+)-ATPase system, and in concentrations from 10(-10) to 10(-5) M enhanced skeletal muscle SR membrane Ca(2+)-ATPase activity in vitro (P < 0.001). Milrinone analogues which have been previously shown to enhance rabbit myocardial membrane Ca(2+)-ATPase activity, and which have a twist relationship of the pyridine rings, were also striated muscle Ca(2+)-ATPase stimulators. We conclude that (1) striated muscle is a mammalian tissue in which physiological levels of biologically relevant thyroid hormone analogues, particularly Dimit, stimulate Ca(2+)-ATPase activity in vitro by a non-genomic mechanism; (2) cardiac bipyridine analogues which are thyromimetic in vitro in rabbit heart, and which have structural homologies with thyroid hormone, are stimulators of rabbit striated muscle sarcoplasmic reticulum Ca(2+)-ATPase activity.
authors.affiliation: Department of Medicine, State University of New York at Buffalo, School of Medicine and Biomedical Sciences.
authors.forename: P R
authors.initials: PR
authors.lastname: Warnick
authors.forename: P J
authors.initials: PJ
authors.lastname: Davis
authors.forename: F B
authors.initials: FB
authors.lastname: Davis
authors.forename: V
authors.initials: V
authors.lastname: Cody
authors.forename: J
authors.initials: J
authors.lastname: Galindo
authors.forename: S D
authors.initials: SD
authors.lastname: Blas
mesh_terms: D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002316:Cardiotonic Agents / Q000494:pharmacology*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology*; D020105:Milrinone; D009132:Muscles / Q000201:enzymology*; D011728:Pyridones / Q000494:pharmacology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013970:Thyronines / Q000494:pharmacology; D013974:Thyroxine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D014284:Triiodothyronine / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D002316:Cardiotonic Agents; D011728:Pyridones; D013970:Thyronines; D014284:Triiodothyronine; C022861:3,5-dimethyl-3'-isopropyl-L-thyronine; D000252:Calcium-Transporting ATPases; D020105:Milrinone; C011126:tetraiodothyroacetic acid; D013974:Thyroxine