Naphthalenesulfonamides such as N-(6-amino-hexyl)-5-chloro-1-naphthalenesulfonamide (W-7) are potent calmodulin (CaM) antagonists and act upon several protein kinases at higher concentration. When the naphthalene ring was replaced by isoquinoline, the derivatives were no longer CaM antagonists but retained the ability to inhibit protein kinases, and some of the derivatives exhibited selective inhibition toward a certain protein kinase. cAMP-dependent, cGMP-dependent, and Ca2+-phospholipid-dependent (protein kinase C) protein kinases were inhibited significantly by addition of 10(-6) M N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide (H-8) and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). H-8 was the most active of the inhibitors in this series and inhibited more markedly cyclic nucleotide dependent protein kinases, than other kinases, while the derivative with the sulfonylpiperazine residue (H-7) was the most potent in inhibiting protein kinase C. Apparent Ki values of H-8 were 0.48 and 1.2 microM for cGMP-dependent and cAMP-dependent protein kinases, respectively, and the Ki value of H-7 for protein kinase C was 6 microM. Both the holoenzyme and the catalytic subunit (or fragment), which is active without an enzyme activator, are susceptible to these compounds with a similar concentration dependency, thereby indicating that the inhibitory effect is attributed to the direct interaction of the compound with the active center of the enzyme but not with the enzyme activator. The inhibitions were freely reversible and of the competitive type with respect to ATP and of the noncompetitive type with respect to the phosphate acceptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Isoquinolinesulfonamides, novel and potent inhibitors of cyclic nucleotide dependent protein kinase and protein kinase C.

Introduction. ............................................................ 129 Fiber Types. ............................................................ 130 Historical introduction. ................................................. 130 Classification and terminology. ........................................... 131 Contractile properties of different types of fiber. ............................ 134 Mechanical Properties. .................................................... 138 Introduction ........................................................... 138 Series-elastic component. ................................................ 138 Length : tension relation of contractile material. ............................. 140 Force: velocity properties of contractile component. ......................... 145 Behavior of series-elastic and contractile components in isotonic and isometric contractions ....................................................... 147 Active state, time course of isometric twitch, and posttetanic potentiation ....... 149 Ontogenetic Differentiation of Fast and Slow Muscles. ......................... 161 Growth ............................................................... 161 Dynamic properties. .................................................... 163 Other developmental changes. .......................................... 166 Kelation Between Size and Speed of Contraction .............................. 166 Speed of contraction of homologous muscles of different species. ............. 166 Speed of contraction of different muscles of same animal. .................... 169 Neural Control of Dynamic Properties. ...................................... 170 Introductiorl ........................................................... 170 Dynamic properties of normal and cross-innervated muscles .................. 172 Effects of nerve cross-union on properties of myosin. ......................... 175 Neural influences on noncontractile structures in muscle cells ................. 176 Correlations Between Dynamic and Chemical Properties of Contractile Material. .. 177 Introduction ........................................................... 177 Structure of myosin. .................................................... 177 Relation between ATPase activity of myosin and intrinsic speed of shortening . 181 Functional differences between fast and slow muscles. ....................... 182 Review of Some Major Problems ........................................... 183

Dynamic properties of mammalian skeletal muscles.

Ca(2+) regulation of contraction in vertebrate striated muscle is exerted primarily through effects on the thin filament, which regulate strong cross-bridge binding to actin. Structural and biochemical studies suggest that the position of tropomyosin (Tm) and troponin (Tn) on the thin filament determines the interaction of myosin with the binding sites on actin. These binding sites can be characterized as blocked (unable to bind to cross bridges), closed (able to weakly bind cross bridges), or open (able to bind cross bridges so that they subsequently isomerize to become strongly bound and release ATP hydrolysis products). Flexibility of the Tm may allow variability in actin (A) affinity for myosin along the thin filament other than through a single 7 actin:1 tropomyosin:1 troponin (A(7)TmTn) regulatory unit. Tm position on the actin filament is regulated by the occupancy of NH-terminal Ca(2+) binding sites on TnC, conformational changes resulting from Ca(2+) binding, and changes in the interactions among Tn, Tm, and actin and as well as by strong S1 binding to actin. Ca(2+) binding to TnC enhances TnC-TnI interaction, weakens TnI attachment to its binding sites on 1-2 actins of the regulatory unit, increases Tm movement over the actin surface, and exposes myosin-binding sites on actin previously blocked by Tm. Adjacent Tm are coupled in their overlap regions where Tm movement is also controlled by interactions with TnT. TnT also interacts with TnC-TnI in a Ca(2+)-dependent manner. All these interactions may vary with the different protein isoforms. The movement of Tm over the actin surface increases the "open" probability of myosin binding sites on actins so that some are in the open configuration available for myosin binding and cross-bridge isomerization to strong binding, force-producing states. In skeletal muscle, strong binding of cycling cross bridges promotes additional Tm movement. This movement effectively stabilizes Tm in the open position and allows cooperative activation of additional actins in that and possibly neighboring A(7)TmTn regulatory units. The structural and biochemical findings support the physiological observations of steady-state and transient mechanical behavior. Physiological studies suggest the following. 1) Ca(2+) binding to Tn/Tm exposes sites on actin to which myosin can bind. 2) Ca(2+) regulates the strong binding of M.ADP.P(i) to actin, which precedes the production of force (and/or shortening) and release of hydrolysis products. 3) The initial rate of force development depends mostly on the extent of Ca(2+) activation of the thin filament and myosin kinetic properties but depends little on the initial force level. 4) A small number of strongly attached cross bridges within an A(7)TmTn regulatory unit can activate the actins in one unit and perhaps those in neighboring units. This results in additional myosin binding and isomerization to strongly bound states and force production. 5) The rates of the product release steps per se (as indicated by the unloaded shortening velocity) early in shortening are largely independent of the extent of thin filament activation ([Ca(2+)]) beyond a given baseline level. However, with a greater extent of shortening, the rates depend on the activation level. 6) The cooperativity between neighboring regulatory units contributes to the activation by strong cross bridges of steady-state force but does not affect the rate of force development. 7) Strongly attached, cycling cross bridges can delay relaxation in skeletal muscle in a cooperative manner. 8) Strongly attached and cycling cross bridges can enhance Ca(2+) binding to cardiac TnC, but influence skeletal TnC to a lesser extent. 9) Different Tn subunit isoforms can modulate the cross-bridge detachment rate as shown by studies with mutant regulatory proteins in myotubes and in in vitro motility assays. (ABSTRACT TRUNCATED)

https://www.physiology.org/doi/pdf/10.1152/physrev.2000.80.2.853

Regulation of Contraction in Striated Muscle

Inhibition of forskolin-induced neurite outgrowth and protein phosphorylation by a newly synthesized selective inhibitor of cyclic AMP-dependent protein kinase, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), of PC12D pheochromocytoma cells.

The dystrophin-glycoprotein complex was tested for interaction with several components of the extracellular matrix as well as actin. The 156-kD dystrophin-associated glycoprotein (156-kD dystroglycan) specifically bound laminin in a calcium-dependent manner and was inhibited by NaCl (IC50 = 250 mM) but was not affected by 1,000-fold (wt/wt) excesses of lactose, IKVAV, or YIGSR peptides. Laminin binding was inhibited by heparin (IC50 = 100 micrograms/ml), suggesting that one of the heparin-binding domains of laminin is involved in binding dystroglycan while negatively charged oligosaccharide moieties on dystroglycan were found to be necessary for its laminin-binding activity. No interaction between any component of the dystrophin-glycoprotein complex and fibronectin, collagen I, collagen IV, entactin, or heparan sulfate proteoglycan was detected by 125I-protein overlay and/or extracellular matrix protein-Sepharose precipitation. In addition, laminin-Sepharose quantitatively precipitated purified dystrophin-glycoprotein complex, demonstrating that the laminin-binding site is accessible when dystroglycan is associated with the complex. Dystroglycan of nonmuscle tissues also bound laminin. However, the other proteins of the striated muscle dystrophin-glycoprotein complex appear to be absent, antigenically dissimilar or less tightly associated with dystroglycan in nonmuscle tissues. Finally, we show that the dystrophin-glycoprotein complex cosediments with F-actin but does not bind calcium or calmodulin. Our results support a role for the striated muscle dystrophin-glycoprotein complex in linking the actin-based cytoskeleton with the extracellular matrix. Furthermore, our results suggest that dystrophin and dystroglycan may play substantially different functional roles in nonmuscle tissues.

/pdf/a-role-for-the-dystrophin-glycoprotein-complex-as-a-177ni02c2i.pdf

A role for the dystrophin-glycoprotein complex as a transmembrane linker between laminin and actin

1. The low-molecular-weight components of myosin freshly prepared by the standard procedure from adult rabbit skeletal muscle migrated as four main bands Ml1, Ml2, Ml3 and Ml4 on polyacrylamide-gel electrophoresis in 8m-urea. 2. The number of bands increased on storage. This change was accelerated by increasing the temperature and pH. 3. None of the bands had electrophoretic mobilities identical with those of the well-characterized proteins of the myofibril or with the sarcoplasmic proteins. 4. By varying the ionic conditions and concentration of muscle mince used for the initial extraction it was possible to change the relative proportions of the two electrophoretic bands of intermediate mobility, Ml2 and Ml3. 5. The four-band picture similar to that obtained with rabbit was observed with myosin isolated from skeletal muscle of the rat, mouse, hamster, pigeon and chicken. 6. Rabbit cardiac myosin gave only two bands on electrophoresis. Myosin from rabbit red muscle gave a pattern intermediate between cardiac and white-skeletal-muscle myosin, i.e. the two fastest bands were present in decreased relative amounts. 7. It is suggested that the differences in the low-molecular-weight components of myosin from different types of muscle are a consequence of differences in the isoenzyme composition of the myosins.

/pdf/an-electrophoretic-study-of-the-low-molecular-weight-rar3816uqc.pdf

An electrophoretic study of the low-molecular-weight components of myosin.

Tropomyosin (TM) is widely distributed in all cell types associated with actin as a fibrous molecule composed of two α-helical chains arranged as a coiled-coil. It is localised, polymerised end to end, along each of the two grooves of the F-actin filament providing structural stability and modulating the filament function. To accommodate the wide range of functions associated with actin filaments that occur in eucaryote cells TM exists in a large number isoforms, over 20 of which have been identified. These isoforms which are expressed by alternative promoters and alternative RNA processing of four genes, TPM1, 2, 3 and 4, all conform to a general pattern of structure. Their amino acid sequences consist of an integral number, six or seven in vertebrates, of quasiequivalent regions of about 40 residues that are considered to represent the actin-binding regions of the molecule. In addition to the variable regions a large part of the polypeptide chains of the TM isoforms, mainly centrally located and expressed by five exons, is invariant. Many of the isoforms are tissue and filament specific in their distribution implying that the exons expressed in them and the regions of the molecule they represent are of significance for the function of the filament system with which they are associated. In the case of muscle there is clear evidence that the TM moves its position on the F-actin filament during contraction and it is therefore considered to play an important part in the regulation of the process. It is uncertain how the role of TM in muscle compares to that in non-muscle systems and if its function in the former tissue is unique to muscle.

Vertebrate tropomyosin: distribution, properties and function.

THE regulation of contractile activity in cardiac muscle by changes in the intracellular Ca2+ concentration involves the regulatory protein system, consisting of tropomyosin and the troponin complex that is located in the I filament. Although the regulatory protein system of cardiac muscle is essentially similar in function to that of skeletal muscle, the components differ in the two tissues. Cardiac tropomyosin consists principally of α subunits, whereas the skeletal protein is composed of α and β subunits1. Troponin I, troponin C and troponin T are all specific for cardiac muscle in that they have different chemical and immunochemical properties from the corresponding skeletal muscle proteins2–4. In addition, cardiac troponin I and cardiac troponin C have been shown to have different amino acid sequences from their skeletal muscle counterparts3,5.

Phosphorylation of troponin I and the inotropic effect of adrenaline in the perfused rabbit heart

Troponin T (TnT) is present in striated muscle of vertebrates and invertebrates as a group of homologous proteins with molecular weights usually in the 31–36kDa range. It occupies a unique role in the regulatory protein system in that it interacts with TnC and TnI of the troponin complex and the proteins of the myofibrillar thin filament, tropomyosin and actin. In the myofibril the molecule is about 18nm long and for much its length interacts with tropomyosin. The ability of TnT to form a complex with tropomyosin is responsible for locating the troponin complex with a periodicity of 38.5nm along the thin filament of the myofibril. In addition to its structural role, TnT has the important function of transforming the TnI–TnC complex into a system, the inhibitory activity of which, on the tropomyosin–actomyosin MgATPase of the myofibril, becomes sensitive to calcium ions. Different genes control the expression of TnT in fast skeletal, slow skeletal and cardiac muscles. In all muscles, and particularly in fast skeletal, alternative splicing of mRNA produces a series of isoforms in a developmentally regulated manner. In consequence TnT exists in many more isoforms than any of the other thin filament proteins, the TnT superfamily. Despite the general homology of TnT isoforms, this alternative splicing leads to variable regions close to the N-␣and C-termini. As the isoforms have slightly different effects on the calcium sensitivity of the actomyosin MgATPase, modulation of the contractile response to calcium can occur during development and in different muscle types. TnT has recently aroused clinical interest in its potential for detecting myocardial damage and the association of mutations in the cardiac isoform with hypertrophic cardiomyopathy.

Troponin T: genetics, properties and function

1. Free thiol groups were shown to be essential for tropomyosin to effect maximum inhibition of the Ca(2+)-stimulated ATPase (adenosine triphosphatase) of desensitized actomyosin but not for its activity in the regulatory-protein system. 2. The activity of tropomyosin on the Mg(2+)-stimulated ATPase in the regulatory-protein system was more susceptible to enzymic digestion and thermal denaturation than its effect on the Ca(2+)-stimulated ATPase of actomyosin. 3. Rabbit skeletal tropomyosin migrated as two distinct electrophoretic components in the presence of sodium dodecyl sulphate and urea and as four components on isoelectric focusing in urea. 4. The two main subunits present in rabbit skeletal tropomyosin, which have been named the alpha- and beta-chains, were separated by chromatography on CM-cellulose in urea at pH4.0. They were shown to be virtually identical in amino acid composition, except for their cysteine contents. The alpha(2) and beta(2) forms of tropomyosin possessed all the biological activities characteristic of normal tropomyosin preparations. 5. In skeletal muscle the alpha and beta components of tropomyosin were present in the proportion of 4:1. Somewhat lower ratios were obtained in skeletal muscle of sheep, pig and cow. 6. Tropomyosin isolated from cardiac muscle and Pecten maximus adductor muscle migrated as one band only. These tropomyosins possessed similar biological activities to those isolated from skeletal muscle.

S. V. Perry

Papers

An electrophoretic study of the low-molecular-weight components of myosin.

Vertebrate tropomyosin: distribution, properties and function.

Phosphorylation of troponin I and the inotropic effect of adrenaline in the perfused rabbit heart

Troponin T: genetics, properties and function

The subunits and biological activity of polymorphic forms of tropomyosin