Search PubMed⌕ Search

Biomedical subjects

F J Samaha

Publications and source records attributed to F J Samaha.

At least 37 records · Page 2Linked to original sources
PubMed1983

Mechanism of the stimulation of Ca2+-dependent ATPase of skeletal muscle sarcoplasmic reticulum by protein kinase.

Sarcoplasmic reticulum isolated from moderately fast rabbit skeletal muscle contains intrinsic adenosine 3',5'-monophosphate (cAMP)-independent protein kinase activity and a substrate of 100 000 Mr. Phosphorylation of skeletal sarcoplasmic reticulum by either endogenous membrane bound or exogenous cAMP-dependent protein kinase results in stimulation of the initial rates of Ca2+ transport and Ca2+-ATPase activity. To determine the molecular mechanism by which protein kinase-dependent phosphorylation regulates the calcium pump in skeletal sarcoplasmic reticulum, we examined the effects of protein kinase on the individual steps of the Ca2+-ATPase reaction sequence. Skeletal sarcoplasmic reticulum vesicles were preincubated with cAMP and cAMP-dependent protein kinase in the presence (phosphorylated sarcoplasmic reticulum) and absence (control sarcoplasmic reticulum) of adenosine 5'-triphosphate (ATP). Control and phosphorylated sarcoplasmic reticulum were subsequently assayed for formation (5-100 ms) and decomposition (0-73 ms) of the acid-stable phosphorylated enzyme (E approximately P) of Ca2+-ATPase. Protein kinase mediated phosphorylation of skeletal sarcoplasmic reticulum resulted in pronounced stimulation of initial rates and levels of E approximately P in sarcoplasmic reticulum preincubated with either ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA) prior to assay (Ca2+-free sarcoplasmic reticulum), or with calcium/EGTA buffer (Ca2+-bound sarcoplasmic reticulum). These effects were evident within a wide range of ionized Ca2+. Phosphorylation of skeletal sarcoplasmic reticulum by protein kinase also increased the initial rate of E approximately P decomposition. These findings suggest that protein kinase-dependent phosphorylation of skeletal sarcoplasmic reticulum regulates several steps in the Ca2+-ATPase reaction sequence which result in an overall stimulation of the active calcium transport observed at steady state.

Animals↗
PubMed1982

Creatine kinase activity in normal and Duchenne muscular dystrophy fibroblasts.

Cultured human skin fibroblasts from 9 patients with Duchenne muscular dystrophy (DMD) and 8 normal age- and sex-matched controls were examined for creatine kinase (CK) activity. Both the normal and the DMD fibroblasts were found to have significant levels of CK activity (approximately 10 x 10(-3) IU per milligram of fibroblast protein). The control cells had slightly higher CK activity than the DMD lines, but this difference was not significant (0.2 less than P less than 0.1). The MM (muscle) isozyme, the BB (brain) isozyme, and the MB (hybrid) isozyme, of CK were found to be present in fibroblasts. The isozymes were separated by electrophoresis and the relative amount of each was determined for both normal and DMD cells. In normal fibroblasts, approximately 48% of the total CK activity was of the MM type, 40% was of the BB type, and 12% was of the MB type with no significant differences apparent between normal and DMD groups. The presence in human fibroblasts of significant levels of CK activity with a characteristic isozyme profile is an important consideration for studies of this "marker" enzyme in the pseudohypertrophic muscle of DMD.

Adolescent↗
PubMed1982

Partial biochemical maturation of aneurally cultured human skeletal muscle.

We studied cultures of human skeletal muscle in vitro and established standards for biochemical markers of cellular differentiation. DNA synthesis ceased at the time of fusion, implying the absence of fibroblasts. Myosin heavy-chain synthesis, creatine and pyruvate kinase activities, and isoenzymes of creatine kinase were measured serially over 36 days. Filamin and fibronectin proteins were identified in these cultures. Compared to chick muscle in culture, human skeletal muscle cells remained relatively immature. These data provide a basis for the study of diseased human muscle cells in culture.

Animals↗
PubMed1981

Duchenne muscular dystrophy: adenosine triphosphate and creatine phosphate content in muscle.

In carrying out a new study of nucleotide concentrations in dystrophic muscle, we utilized myosin as a reference base. In nine control vastus lateralis muscle samples, nucleotide concentrations were 105 +/- 11 (SEM) moles of adenosine triphosphate (ATP) and 446 +/- 57 (SEM) nmoles of creatine phosphate (CP) per milligram of myosin. In seven Duchenne dystrophic vastus lateralis muscle samples, nucleotide concentrations were 127 +/- 25 (SEM) nmoles of ATP and 462 +/- 119 (SEM) moles of CP per milligram of myosin. The CP:ATP ratio of 3.6 +/- 0.367 from Duchenne muscle was not significantly different from normal, 4.32 +/- 0.243 ((p less than 0.20). In addition, myokinase activity, which is automatically assayed in these assays, was significantly increased in the Duchenne samples (p less than 0.10). The percent of myosin per total protein in the Duchenne biopsies was also diminished by 29% (p less than 0.01). These studies suggest that ATP and CP concentrations are not decreased in Duchenne dystrophic muscle when expressed in relation to the amount of contractile protein.

Adenosine Triphosphate↗
PubMed1979

Myosin light chains in Duchenne dystrophy and paraplegic muscle.

Myosin light chains were isolated from cat gastrocnemius and soleus muscles rendered paraplegic for 1 year and from the vastus lateralis of six patients with Duchenne muscular dystrophy. Despite the altered pattern of function of these muscles, no alterations were noted in the type or relative proportion of these myosin light chains when compared to control muscles.

Animals↗