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)

1. We tested the hypotheses that coupling between oxidative metabolism and force in noradrenaline (NOR)-activated rabbit aorta is controlled (a) by an energy-dependent step or steps in receptor-operated coupling mechanisms upstream to myosin light chain (MLC) kinase, or (b) by energy limitation of MLC kinase-mediated phosphorylation of the MLC or actin-activated myosin ATPase. 2. Oxidative energy production was rapidly inhibited by decreasing organ bath PO2 to less than 30 mmHg. There was no difference, comparing KCl- or NOR-induced force, in the rates of decrease of [PCr] (phosphocreatine) or [ATP] following inhibition of oxidative energy production. (In this report we use the term [PCr] and [ATP] to indicate mean tissue values). Initial rates of decrease in [PCr] and [ATP] following inhibition of oxidative energy production were 0.05 mM/min and 0.06 mM/min, respectively. 3. Despite similar decreases in mean tissue [PCr] and [ATP], relaxations of KCl-induced contractions following inhibition of oxidative energy production were markedly delayed and were blunted compared to relaxations seen during NOR-induced contractions. The threshold mean tissue [PCr] and [ATP] for relaxation during KCl stimulation were 0.25 and 0.60 to 0.80 mM, respectively. During NOR stimulation, threshold values of [PCr] and [ATP] were 0.50 mM and 0.80 mM, respectively. Mean tissue [PCr] and [ATP] levels at 50% relaxation of KCl-induced force were less than 0.1 mM and 0.1 mM, respectively. Fifty per cent relaxation of NOR-induced force occurred at [PCr] and [ATP] values of 0.35 mM and 0.65 mM, respectively. 4. MLC phosphorylation levels decreased during relaxation of NOR force evoked by inhibition of oxidative energy production. There was no change in the level of MLC phosphorylation following inhibition of oxidative energy production in KCl-contracted muscle even at mean tissue [PCr] and [ATP] lower than values associated with decreases in MLC phosphorylation during relaxations of NOR-induced force. 5. Oxygen-induced redevelopment of force during NOR exposure was not dependent on extracellular Ca2+. Mean tissue [PCr] increased prior to onset of O2-evoked force redevelopment. Increases in MLC phosphorylation were seen at the time of onset of force redevelopment. 6. Oxidative metabolism-contraction coupling during NOR-stimulation seems not to be due to energy limitation of the MLC kinase reaction or actin-activated myosin ATPase. Data suggest the rate-limiting step is an energy-dependent reaction in receptor-operated coupling mechanisms upstream to MLC kinase.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Rate-limiting energy-dependent steps controlling oxidative metabolism-contraction coupling in rabbit aorta. 153 69

We investigated the mode of relaxant effects of cytochalasin D, a capping agent of actin filaments, on contractile responses in the rat aorta and chicken gizzard smooth muscles. Cytochalasin D inhibited the contraction induced by high K+ or noradrenaline (10 nM-1 microM) without changing cytosolic Ca2+ level ([Ca2+]i) in the rat aorta. In the absence of external Ca2+, 12-deoxyphorbol 13-isobutylate (DPB) (1 microM) induced sustained contraction without increasing in [Ca2+]i and cytochalasin D also inhibited this contraction. In the permeabilized chicken gizzard smooth muscle, cytochalasin D inhibited the Ca2+ (1-10 microM)-induced contraction. Cytochalasin D also inhibited the Ca(2+)-independent contraction in the muscle which had been thiophosphorylated by ATP gamma S. Cytochalasin D decreased the velocity of superprecipitation in the chicken gizzard native actomyosin (myosin B) affecting neither the level of MLC phosphorylation nor Mg(2+)-ATPase activity. These results suggest that cytochalasin D inhibits smooth muscle contractions without any effect on the Ca(2+)-dependent MLC phosphorylation or subsequent activation of myosin ATPase activity. Based on these evidences, it is concluded that cytochalasin D may inhibit smooth muscle contraction possibly through uncoupling of the force generation from the activated actomyosin Mg(2+)-ATPase.
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PMID:Cytochalasin D inhibits smooth muscle contraction by directly inhibiting contractile apparatus. 884 66