Forgotten research from 19th century: science should not follow fashion.

The fine structure of cross-striated muscle and its changes during contraction were known already in considerable detail in the 19th century. This knowledge was the result of studying birefringence properties of muscle fibres under the polarization microscope, a method mainly established by Brücke (Denk Kais Akad Wiss Math Naturwiss Cl 15:69-84, 1858) in Vienna, Austria. The knowledge was seemingly forgotten in the first half of the 20th century before it was rediscovered in 1954.

Human skeletal muscle: transition between fast and slow fibre types.

Human skeletal muscles consist of different fibre types: slow fibres (slow twitch or type I) containing the myosin heavy chain isoform (MHC)-I and fast fibres (fast twitch or type II) containing MHC-IIa (type IIA) or MHC-IId (type IID). The following order of decreasing kinetics is known: type IID > type IIA >> type I. This order is especially based on the kinetics of stretch activation, which is the most discriminative property among fibre types.

The highly efficient holding function of the mollusc 'catch' muscle is not based on decelerated myosin head cross-bridge cycles.

Certain smooth muscles are able to reduce energy consumption greatly when holding without shortening. For instance, this is the case with muscles surrounding blood vessels used for regulating blood flow and pressure. The phenomenon is most conspicuous in 'catch' muscles of molluscs, which have been used as models for investigating this important physiological property of smooth muscle.

Twitchin of mollusc smooth muscles can induce "catch"-like properties in human skeletal muscle: support for the assumption that the "catch" state involves twitchin linkages between myofilaments.

Molluscan catch muscles can maintain tension with low or even no energy utilization, and therefore, they represent ideal models for studying energy-saving holding states. For many decades it was assumed that catch is due to a simple slowing of the force-generating myosin head cross-bridge cycles. However, recently evidences increased suggesting that catch is rather caused by passive structures linking the myofilaments in a phosphorylation-dependent manner.

Qualitatively different cross-bridge attachments in fast and slow muscle fiber types.

Contractile properties differ between skeletal, cardiac and smooth muscles as well as between various skeletal muscle fiber types. This functional diversity is thought to be mainly related to different speeds of myosin head pulling cycles, with the molecular mechanism of force generation being essentially the same. In this study, force-generating attachments of myosin heads were investigated by applying small perturbations of myosin head pulling cycles in stepwise stretch experiments on skeletal muscle fibers of different type.

Molecular basis of the catch state in molluscan smooth muscles: a catchy challenge.

The catch state (or 'catch') of molluscan smooth muscles is a passive holding state that occurs after cessation of stimulation. During catch, force and, in particular, resistance to stretch are maintained for long time periods with low (or no) energy consumption at basal intracellular free [Ca2+]. The catch state is initiated by Ca2+-stimulated dephosphorylation of the titin-like protein twitchin and is inhibited by cAMP-dependent phosphorylation of twitchin.

Influence of fast and slow alkali myosin light chain isoforms on the kinetics of stretch-induced force transients of fast-twitch type IIA fibres of rat.

This study contributes to understand the physiological role of slow myosin light chain isoforms in fast-twitch type IIA fibres of skeletal muscle. These isoforms are often attached to the myosin necks of rat type IIA fibres, whereby the slow alkali myosin light chain isoform MLC1s is much more frequent and abundant than the slow regulatory myosin light chain isoform MLC2s. In the present study, single-skinned rat type IIA fibres were maximally Ca(2+) activated and subjected to stepwise stretches for causing a perturbation of myosin head pulling cycles.

The catch state of mollusc catch muscle is established during activation: experiments on skinned fibre preparations of the anterior byssus retractor muscle of Mytilus edulis L. using the myosin inhibitors orthovanadate and blebbistatin.

Catch is a holding state of muscle where tension is maintained passively for long time periods in the absence of stimulation. The catch state becomes obvious after termination of activation; however, it is possible that catch linkages are already established during activation. To investigate this, skinned fibre bundles of the anterior byssus retractor muscle of Mytilus edulis were maximally activated with Ca(2+) and subsequently exposed to 10 mmol l(-1) orthovanadate (V(i)) or 5 mumol l(-1) blebbistatin to inhibit the force-generating myosin head cross-bridges.

Myosin heavy chain isoform composition and stretch activation kinetics in single fibres of Xenopus laevis iliofibularis muscle.

Skeletal muscle is composed of specialized fibre types that enable it to fulfil complex and variable functional needs. Muscle fibres of Xenopus laevis, a frog formerly classified as a toad, were the first to be typed based on a combination of physiological, morphological, histochemical and biochemical characteristics. Currently the most widely accepted criterion for muscle fibre typing is the myosin heavy chain (MHC) isoform composition because it is assumed that variations of this protein are the most important contributors to functional diversity.

Fine-tuning of cross-bridge kinetics in cardiac muscle of rat and mouse by myosin light chain isoforms.

Cross-bridge kinetics underlying stretch-induced force transients was studied in cardiac muscle strips with different myosin heavy chain (MHC) and myosin light chain (MLC) isoforms. The force transients were induced by stepwise stretches of maximally Ca(2+)-activated skinned muscle strips. The MHC and MLC isoforms were analyzed by electrophoreses after the mechanical experiments.

Effect of pH on the rate of myosin head detachment in molluscan catch muscle: are myosin heads involved in the catch state?

Moderate alkalisation is known to terminate the catch state of bivalve mollusc smooth muscles such as the anterior byssus retractor muscle (ABRM) of Mytilus edulis L. In the present study, we investigated the effect of moderate alkalisation (pH 7.2-7.

Dependence of cross-bridge kinetics on myosin light chain isoforms in rabbit and rat skeletal muscle fibres.

Cross-bridge kinetics underlying stretch-induced force transients was studied in fibres with different myosin light chain (MLC) isoforms from skeletal muscles of rabbit and rat. The force transients were induced by stepwise stretches (< 0.3% of fibre length) applied on maximally Ca2+-activated skinned fibres.

Elementary steps of the cross-bridge cycle in fast-twitch fiber types from rabbit skeletal muscles.

To understand the molecular mechanism underlying the diversity of mammalian skeletal muscle fibers, the elementary steps of the cross-bridge cycle were investigated in three fast-twitch fiber types from rabbit limb muscles. Skinned fibers were maximally Ca(2+)-activated at 20 degrees C and the effects of MgATP, phosphate (P, P(i)), and MgADP were studied on three exponential processes by sinusoidal analysis. The fiber types (IIA, IID, and IIB) were determined by analyzing the myosin heavy-chain isoforms after mechanical experiments using high-resolution SDS-PAGE.

No effect of twitchin phosphorylation on the rate of myosin head detachment in molluscan catch muscle: are myosin heads involved in the catch state?

Phosphorylation of twitchin is known to abolish the catch state of anterior byssus retractor muscle (ABRM) of the bivalve mollusc Mytilus edulis. To investigate the role of myosin head involvement in force maintenance during catch, the effect of twitchin phosphorylation on myosin head detachment was studied in saponin-skinned fibre bundles of ABRM. The detachment rate of myosin heads was deduced from two types of experiments: (1) force decay after stepwise stretch of maximally Ca2+-activated fibre bundles (pCa 4.

Effects of vanadate, phosphate and 2,3-butanedione monoxime (BDM) on skinned molluscan catch muscle.

The effects of orthovanadate (V(i)), inorganic phosphate (P(i)) and 2,3-butanedione monoxime (BDM) on tension, force transients and the catch state (passive tension maintenance) were investigated in saponin-skinned fibre bundles of the anterior byssus retractor muscle (ABRM) of the bivalve mollusc Mytilus edulis at pH 6.7. During maximal Ca(2+) activation isometric force was depressed by V(i) (0.

Kinetic properties of myosin heavy chain isoforms in mouse skeletal muscle: comparison with rat, rabbit, and human and correlation with amino acid sequence.

Stretch activation kinetics were investigated in skinned mouse skeletal muscle fibers of known myosin heavy chain (MHC) isoform content to assess kinetic properties of different myosin heads while generating force. The time to peak of stretch-induced delayed force increase (t(3)) was strongly correlated with MHC isoforms [t(3) given in ms for fiber types containing specified isoforms; means +/- SD with n in parentheses: MHCI 680 +/- 108 (13), MHCIIa 110.5 +/- 10.

Fiber type conversion alters inactivation of voltage-dependent sodium currents in murine C2C12 skeletal muscle cells.

Each skeletal muscle of the body contains a unique composition of "fast" and "slow" muscle fibers, each of which is specialized for certain challenges. This composition is not static, and the muscle fibers are capable of adapting their molecular composition by altered gene expression (i.e.

Functional properties of skinned rabbit skeletal and cardiac muscle preparations containing alpha-cardiac myosin heavy chain.

Contractile properties of skinned muscle fibres from the masseter muscle and strips of heart atrium muscle from rabbits, both containing the alpha-cardiac myosin heavy chain isoform (alpha-cardiac MHC), were investigated and compared with those of other skeletal muscle fibre types. The stretch-induced delayed force increase (stretch activation) was investigated on maximally Ca(2+)-activated skinned preparations as an index of the kinetic properties of the myosin heads of various MHC isoforms. Skeletal muscle fibres containing exclusively alpha-cardiac MHC (type alpha) and muscle strips of heart atrium showed specific kinetics of stretch activation intermediate between those of types IIA and I fibres.

Slowing effects of Mg2+ on contractile kinetics of skinned preparations of rat hearts depending on myosin heavy chain isoform content.

The effects of changes in Mg2+ concentration on the kinetics of stretch activation were investigated on skinned rat heart preparations under maximal Ca2+ activation. Muscle strips of hyper- and hypothyroid rat hearts were investigated at 0.5 and 1 mM free Mg2+; the total ATP concentration was 8 mM which resulted in saturating MgATP2- concentrations above 5 mM.

Functional differences in type-I fibres from two slow skeletal muscles of rabbit.

The present study addressed the question of whether the slow fibres of mammalian skeletal muscle, containing the myosin heavy chain MHCI (type-I fibres), are a functionally homogeneous population. We compared various properties of Ca(2+)-activated, skinned, type-I fibres from the soleus and semitendinosus muscles of a rabbit. Soleus type-I fibres showed significantly faster kinetics of stretch activation, measured as the time-to-peak of the stretch-induced, delayed force increase, t(3), than semitendinosus fibres (1239+/-438 ms, n=136, vs.

Kinetic properties of cardiac myosin heavy chain isoforms in rat.

The head portion of the myosin heavy chain (MHC) is essential in force generation. As previously shown, Ca2+-activated fibres of mammalian skeletal muscle display a strong correlation between their MHC isoform complement and the kinetics of stretch activation, suggesting isoform-specific differences in kinetic properties of myosin heads. Using the same methodology on muscle strips of atria and ventricles of hyper- and hypothyroid rats, this study showed that the kinetics of cardiac alphaMHC are 3 times faster than those of cardiac betaMHC under isometric conditions and maximal Ca2+ activation.