Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.6.4.1 (myosin ATPase)
 1,140 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The purpose of this study was to determine if selected biochemical parameters representing the contractile and calcium regulating systems of cardiac muscle scaled among mammals having inherently different resting heart rates (RHR). Eight mammalian species with RHR ranging from 51 to 475 beats per minute (bpm) were studied. The oxidative capacity of the myocardium is highly correlated with the RHR. The hypothesis of the present study was that the capacities of the energy utilizing processes of contraction and calcium regulation would also be correlated to the functional demand imposed on the muscle as represented by the RHR. Myosin (M) and myofibrillar (MF) ATPase activities, myosin isoenzyme distribution and sarcoplasmic reticulum (SR) ATPase activity were determined. Animals with RHR above 300 bpm express V1 myosin while animals with lower RHR express primarily V3. M and MF ATPase activities correlated with RHR, but the major difference in activities occurred at the 'threshold' RHR of about 300 bpm at which the switch from V3 to V1 appears to occur. SR ATPase activity per mg of microsomal protein was for the most part constant among different mammals, but the SR ATPase activity per g of heart tissue was significantly correlated with RHR as slower beating hearts tended to yield less SR protein per unit mass. We conclude that both the contractile and calcium regulating systems are scaled to the functional parameter of RHR among different mammals. The contractile system uses a slow myosin ATPase isoform at low resting heart rates whereas above the postulated threshold RHR of about 300 bpm a switch in gene expression to a fast myosin ATPase isoform occurs.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Contractile and calcium regulating capacities of myocardia of different sized mammals scale with resting heart rate. 165 10

Phospholamban, originally described as a cardiac sarcoplasmic reticulum protein, was localized in cryostat sections of three adult canine skeletal muscles (gracilis, extensor carpi radialis, and superficial digitalis flexor) by immunofluorescence labeling with highly specific phospholamban antibodies. Only some myofibers were strongly labeled with phospholamban antibodies. The labeling of myofibers with phospholamban antibodies was compared to the distribution of Type I (slow) and Type II (fast) myofibers as determined by staining adjacent sections cytochemically for the alkali-stable myosin ATPase, a specific marker for Type II myofibers. All the skeletal myofibers labeled for phospholamban above background levels corresponded to Type I (slow) myofibers. The presence of phospholamban in microsomal fractions isolated from canine superficial digitalis flexor (89 +/- 3% Type I) and extensor carpi radialis skeletal muscle (14 +/- 6% Type I) was confirmed by immunoblotting. Antiserum to cardiac phospholamban bound to proteins of apparent Mr values of 25,000 (oligomeric phospholamban) and 5,000-6,000 (monomeric phospholamban) in sarcoplasmic reticulum vesicles from both muscles. Quantification of phospholamban in sarcoplasmic reticulum vesicles from cardic, slow, and fast skeletal muscle tissues following phosphorylation with [gamma-32P] ATP suggested that superficial digitalis flexor and extensor carpi radialis skeletal muscle contained about 16 and 3%, respectively, as much phospholamban as cardiac muscle per unit of sarcoplasmic reticulum. The presence of phospholamban in both Type I (slow) and cardiac muscle fibers supports the possibility that the Ca2+ fluxes across the sarcoplasmic reticulum in both fiber types are similarly regulated, and is consistent with the idea that the relaxant effect of catecholamines on slow skeletal muscle is mediated in part by phosphorylation of phospholamban.
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PMID:Localization of phospholamban in slow but not fast canine skeletal muscle fibers. An immunocytochemical and biochemical study. 293 38

A new potent vasodilator, nicardipine hydrochloride inhibited oxytocin-induced contraction of rat uterus dose-dependently with an increase in the intracellular cyclic AMP level at the onset of relaxation. Dibutyryl cyclic AMP and papaverine, an inhibitor of cyclic AMP phosphodiesterase (PDEase), also inhibited the contraction. Nicardipine inhibited competitively PDEase in homogenates of rat uterus which exhibited apparently two Km values for cyclic AMP (3.6 micro M and 67.3 micro M) with the Ki of 5.3 micro M and 13.2 micro M, respectively, but had no effect on adenylate cyclase. Nicardipine enhanced calcium uptake by rat uterine microsomes, at concentrations which inhibited oxytocin-induced contraction in the same manner as cyclic AMP. The maximal stimulation by nicardipine of the microsomal calcium uptake was identical substantially to that by cyclic AMP, and both were not additive. Cyclic AMP was also accumulated during the uptake reaction in the presence of nicardipine. On the contrary, neither myosin ATPase nor microsomal Ca2+-dependent ATPase was inhibited directly by nicardipine. These results suggest that the inhibition of oxytocin-induced contraction of rat uterus by nicardipine may be due to an enhancement of microsomal calcium uptake, mediated by cyclic AMP accumulated through the inhibition of PDEase.
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PMID:A possible mechanism for relaxation of rat uterine smooth muscle by nicardipine hydrochloride (YC-93), a new potent vasodilator. 627 30