PubMed Health⌕ Search

Biomedical subjects

J C Rüegg

Publications and source records attributed to J C Rüegg.

At least 109 records · Page 6Linked to original sources
PubMed1985

Modulation of calcium sensitivity in cardiac muscle cells.

In the myocardium the relationship between intracellular free calcium and contraction is not unique but may vary over a wide range. Modulation of calcium sensitivity of the myofibrils may be studied in chemically skinned fibres which are devoid of the sarcoplasmic reticulum and in which the ionic composition of the interfilament space can be controlled and influenced at will. Here we review conditions and mechanisms which either lower or raise the free calcium ion concentration required for half maximal activation of a functionally isolated contractile mechanism.

Animals↗
PubMed1984

Phosphorylation of the myosin light chains and satellite proteins in detergent-skinned arterial smooth muscle.

Isoelectric focusing of extracts prepared from detergent-skinned porcine carotid artery showed that contraction was associated with phosphorylation of the regulatory myosin light chains and two additional proteins of the same apparent molecular weight (20,000). These two proteins, previously described as satellites, did not appear to be artifactually derived from the phosphorylated light chains during electrophoresis. That is, each of the phosphorylated proteins migrated as separate and distinct proteins when subjected to a second cycle of isoelectric focusing. Moreover, relaxation of skinned fibers was associated with dephosphorylation of the light chains and both satellites. These findings suggest that the satellites may represent varients of the light chains per se, or another regulatory protein which is reversibly phosphorylated and dephosphorylated during contraction and relaxation of vascular smooth muscle.

Animals↗
PubMed1984

Skinned smooth muscle: time course of force and ATPase activity during contraction cycle.

The time course of ATPase activity and force has been determined during contraction and relaxation in skinned (hyperpermeable) anterior byssus retractor muscle, ABRM, of Mytilus edulis and compared with corresponding measurements on skinned taenia coli of guinea-pigs. Following a calcium-induced contraction, lowering the [Ca++] to 10(-8) M rapidly reduces ATPase activity within 2 min to resting levels while force declines only to about 30-50% of maximal tension within the same time. Thus slow relaxation is due to a 'catch-like-state' which is common to different kinds of smooth muscles and can be reduced with cAMP in ABRM and by Pi in taenia coli.

Adenosine Triphosphatases↗
PubMed1984

Forskolin inhibits tension development in detergent-treated cardiac muscle fibers.

In detergent-treated cardiac muscle fibers, forskolin, a potent activator of adenylate cyclases, inhibits tension development elicited with submaximal [Ca2+] and increases incorporation of 32P into troponin-I. A similar reduced tension development has been observed after treatment with cAMP or the catalytic subunit of the cAMP-dependent protein kinase. It is concluded that these fibers still contain much of the enzyme cascade involved in evoking a contractile response to beta-adrenergic stimulation.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Tension transients in skinned muscle fibres of insect flight muscle and mammalian cardiac muscle: effect of substrate concentration and treatment with myosin light chain kinase.

Glycerinated single fibres from the dorsal longitudinal muscle of Lethocerus maximus were isometrically contracted in MgATP-salines (10 microM Ca2+; 1.5 mM Mg2+; pH 6.7; 22 degrees C and 20 mM PEP; 100 U/ml pyruvate kinase). The ratio of ATPase activity to tension decreased by a factor of 2 after reducing the ATP-concentration from 15 to 0.5 mM. At all ATP-concentrations (0.5-15 mM), the fibres showed tension adjustments in response to small step changes in length characteristic to an actively contracting muscle: i) an elastic phase which did not depend on ATP-concentration ii) a quick phase of stress relaxation with at least two exponential components; iii) a phase of delayed tension generation. An increase in size of the length step and/or a decrease of ATP-concentration slowed the quick phase and the delayed phase. Similar results have been obtained with skinned cardiac muscle (pig right ventricle). To see, how the isolated contractile system is affected by an increase in the light chain phosphorylation, tension transients were studied in skinned right ventricular muscle fibres before and after incubation with ATP gamma S (2 mM), pure myosin light chain kinase (9 micrograms/ml), Calmodulin (1 microM) and Ca2+ (0.8 microM). While isometric tension development elicited by 20 microM Ca2+ in the ATP salt solution was barely affected in presence of the enzyme, the ATPase activity was decreased by about 25% of the control. There was also a marked decrease (about 50%) in the contraction velocity as determined by the recovery of tension following a quick release. Quick stretches cause an immediate increase in tension followed by a rapid fall and a subsequent rise in tension. The velocity of this tension rise decreased by approximately 30% after incubation with myosin light chain kinase.

Adenosine Triphosphate↗
PubMed1984

Effect of Ca2+-independent myosin light chain kinase on different skinned smooth muscle fibers.

In various skinned smooth muscle fiber preparations, (porcine carotid artery, rat tail artery, chicken gizzard and Taenia coli from guinea pig) a Ca2+-independent myosin light chain kinase (MLCK) initiated a contraction in absence of Ca2+. While the Ca2+ insensitive MLCK was effective on the vertebrate smooth muscles it did not act on the invertebrate skinned skeletal muscle preparation from Limulus and anterior byssus retractor muscle from Mytilus edulis. The results indicate that in vertebrate smooth muscles phosphorylation is sufficient for activation and that there is no obligatory role for an additional mechanism in initiation of contraction.

Adenosine Triphosphate↗
PubMed1984

cGMP and cAMP inhibit tension development in skinned coronary arteries.

The effects of physiological concentrations of cGMP and cAMP on tension development in skinned coronary arteries (Triton X-100) were studied. cGMP inhibited tension elicited at intermediate Ca2+ concentrations at pH 7.0 but not at more acidic or alkaline pH values. cAMP, on the other hand, decreased submaximal tension development independent of pH (from pH 6.5 to pH 7.2). Neither nucleotide affected tension development at maximally activating Ca2+ concentrations.

Animals↗
PubMed1984

Effect of calmodulin, Ca2+, and cAMP protein kinase on skinned tracheal smooth muscle.

The characteristics of contraction and relaxation of membrane skinned smooth muscle from guinea pig trachealis muscle are described. Micromolar Ca2+ elicited reproducible contractions in Mg-ATP salt solution at 20 degrees C. The speed of contraction was much faster at 30 and 37 degrees C, enabling cumulative concentration-response curves to be obtained. At these temperatures, a progressive increase in basal tension occurred in the absence of Ca2+. This tension was active and developed more rapidly at pH 6.7 than at pH 7.0. Calmodulin (0.1-10 microM) greatly increased the speed of contraction and lowered the threshold Ca2+ concentration ([Ca2+]) required to initiate contraction from 0.13 to 0.02 microM Ca2+. Trifluoperazine antagonized responses to Ca2+. Thiophosphorylation with adenosine 5'-O-(3-thiotriphosphate) produced maximum tension development, which was Ca2+-independent. This effect was reversible. The results are compatible with myosin-linked regulation of contraction in which a Ca2+ X calmodulin complex activates myosin light chain kinase to phosphorylate myosin. The catalytic subunit of cAMP-dependent protein kinase strongly inhibited tension development and slowly relaxed fibers contracted with threshold [Ca2+] consistent with an action via phosphorylation of myosin light chain kinase. This effect was extremely slow compared with the rate of relaxation by Ca2+ withdrawal or with relaxation of intact smooth muscle by beta-adrenergic agonists.

Animals↗
PubMed1984

Effect on contractility of skinned fibres from mammalian heart and smooth muscle by a new benzimidazole derivative, 4,5-dihydro-6-[2-(4-methoxyphenyl)-1H-benzimidazol-5-yl]-5-methy l-3(2H )- pyridazinone.

The positive inotropic drug 4,5-dihydro-6-[2-(4-methoxyphenyl)-1H-benzimidazol-5-yl]methyl-3(2 H)- pyridazinone (UD-CG 115 BS) enhances calcium induced contraction of skinned fibres from cardiac muscle probably by increasing the calcium sensitivity of troponin. Submaximal calcium induced contraction of skinned fibres from a smooth muscle (guinea-pig taenia coli) are slightly inhibited.

Animals↗
PubMed1983

Force and force transients in skeletal muscle fibres of the frog skinned by freeze-drying.

A freeze-drying method is described by which single skinned skeletal muscle fibres or fibre bundles can readily be obtained. Skinned fibre segments of the ileofibularis and semitendinous muscles of the frog - activated by means of a rapid increase in the Ca-concentration - showed very stable and reproducible contractions. Complete activation occurred at a Ca-concentration of 1.6 X 10(-6) M and the mid-point of the pCa-tension curve occurred at 6.3 X 10(-7) M. Addition of phosphate (less than or equal to 10(-2) M) had a depressing effect on the speed of the Ca-activated tension development as well as on the maximum tension reached. Addition of caffeine (10(-2) M) had no effect on the tension generation, indicating that the sarcoplasmic reticulum, if present, was not active. The force responses due to rapid length changes applied to the Ca-activated fibre preparations were found to be qualitatively similar to the force responses on intact tissue. This skinning technique might be employed on human biopsies, enabling the measurement of physiological parameters such as for example force and shortening velocity.

Animals↗
PubMed1983

An aortic spontaneously active phosphatase dephosphorylates myosin and inhibits actin-myosin interaction.

Actin-myosin interaction in aortic actomyosin reportedly requires phosphorylation of the 20,000 dalton myosin light chains. A spontaneously active phosphatase which dephosphorylates phosphorylase a and isolated phosphorylated cardiac myosin light chains was extracted from bovine aortic smooth muscle. This enzyme, when added to aortic native actomyosin (a) significantly suppressed phosphorylation of the light chains of the native hexameric smooth muscle myosin, (b) accelerated the rate and increased the magnitude of myosin light chain dephosphorylation in actomyosin that had been prephosphorylated, and (c) markedly attenuated the rate of actin-myosin interaction. These results support the hypothesis that myosin phosphorylation and subsequent actin-myosin interactions (contractility) in vascular smooth muscle may be modulated by spontaneously active aortic phosphatase.

Actins↗
PubMed1983

Effect of calcium-antagonist and calmodulin-antagonist drugs on calmodulin-dependent contractions of chemically skinned vascular smooth muscle from rabbit renal arteries.

1. Renal arteries from rabbits were chemically skinned by incubation with Triton X-100, and subsequently stored in buffered glycerol. 2. In the presence of Mg-ATP, of EGTA-buffered calcium, and of calmodulin, miniature strips of the skinned arteries developed tension the strength of which was approx. 15-20% of that of viable renal arteries. 3. Tension development was dependent on the concentration of both calcium and calmodulin. 4. The effect of eight vasodilator drugs, the majority of them being "calmodulin antagonists" or "calcium antagonists", on the skinned arteries was assessed. In concentrations up to 10(-3) M, verapamil, D-600, and hydralazine proved to be ineffective, and the same was found with the dihydropyridine derivatives, nifedipine and felodipine, at 0.6 X 10(-3) M and 0.8 X 10(-4) M, respectively, i.e. at saturation in a 9:1 contracting buffer/ethanol mixture (v/v). 5. In a concentration-dependent manner, trifluoperazine, W-7, and fendiline relaxed Ca-calmodulin-induced tension or prevented tension development when given prior to the activation by Ca-calmodulin. However, considerably higher concentrations of the drugs were necessary for half-maximal relaxation than the reported concentrations for half-maximal saturation of hydrophobic binding sites at the calmodulin molecule. 6. These findings suggest that at therapeutic blood levels, the vasodilator properties of calcium antagonists and other direct vasodilators cannot be explained by interference with the binding of myosin light chain kinase to calmodulin.

Animals↗
PubMed1983

The dependence of unloaded shortening velocity on Ca++, calmodulin, and duration of contraction in "chemically skinned" smooth muscle.

Unloaded shortening velocity, a mechanical parameter associated with the rate of cross-bridge cycling, was investigated in chemically skinned guinea pig taenia coli and hog carotid artery. Shortening velocity was measured by the technique described by Edman, whereby large length steps are rapidly imposed on the muscle and the time under unloaded conditions is determined from the isometric myograms. Shortening velocity determined in this manner was similar to Vmax from the Hill force-velocity relations reported for both living and skinned taenia coli, and, in the case of carotid artery, was at least as large as that reported for living muscle. The behavior of shortening velocity was qualitatively similar for both preparations. Shortening velocity was strongly temperature dependent, with a Q10 of approximately 3.6. Shortening velocity was found to be dependent on both the Ca++ and calmodulin concentration. In contrast to the dependence of isometric force on Ca++-calmodulin, shortening velocity could be increased further by the addition of Ca++ and/or calmodulin under conditions when isometric force was maximized. Incubation with ATP-gamma S, which presumably maximizes the phosphorylation of myosin, did not increase shortening velocity beyond the maximum value obtained in the presence of Ca++-calmodulin alone. The development of shortening velocity after exposure to high Ca++ solution was found to precede that of isometric force. The steady state value tended to be slightly lower than the maximum shortening velocity, the largest difference observed being less than 1.5-fold. Thus, whereas both isometric force and shortening velocity are dependent on the Ca++-calmodulin concentration in skinned smooth muscle, the dependencies are not identical, differing with respect to temporal development and concentration. These differences may underlie the decline in velocity with maintained isometric force observed in living smooth muscle.

Adenosine Triphosphate↗
PubMed1982

cGMP-dependent protein kinase decreases calcium sensitivity of skinned cardiac fibers.

Chemically skinned (Lubrol WX) cardiac muscle fibers produce half-maximum isometric tension at pCa 6.18 (pH 6.7) in presence of MgATP (10 mM). After addition of cGMP (5 microM) and cGMP-dependent protein kinase (0.1 microM), the pCa required for half-maximum activation is 5.96, while maximum tension is not affected. Similar shifts in the tension/pCa-relationship have been observed after incubation of skinned cardiac muscle fibers with cAMP of catalytic subunit of the cAMP-dependent protein kinase. The shift in the Ca2+-sensitivity is associated with an increased incorporation of radioactivity into a Mr 28000 band (presumably troponin-I) and a Mr 145000 band.

1-Methyl-3-isobutylxanthine↗
PubMed1982

Phosphate and vanadate reduce the efficiency of the chemo-mechanical energy transformation in cardiac muscle.

Trabecular preparations from the hog heart right ventricle were "skinned" by treatment with Lubrol WX and glycerol. Ca++ activated isometric contractions were gradedly relaxed by inorganic phosphate (Pi) in the millimolar range or vanadate (Vi) in the micromolar range while tension cost (ATP split/force generated) was increased by a factor of 1.75. From measurements of force, ATPase activity, immediate stiffness and stretch activation, evidence is provided that the mechanical deactivation and the increase in tension cost may result from an acceleration of the myosin cross-bridge cycle, due to a direct interference of Pi and Vi with the chemomechanical energy transformation at the contractile proteins. The possible significance of such a mechanism in cardiac failure or muscle fatigue is discussed.

Animals↗