A morphometric analysis of regional differences in myotomal muscle ultrastructure in the juvenile eel (Anguilla anguilla L.)

Summary Subpopulations of fast and slow fibres within the trunk musculature of elvers were examined using morphometric analysis of electron micrographs. Fibre regions were characterised by their histochemical staining characteristics, and individual fibres located using a coordinate mapping system utilising morphological features as reference points. Percentages of fibre volume occupied by mitochondria, myofibrils, sarcoplasmic reticulum (S.R.), and T-system were determined in each of the fibre groups, along a transect from the skin to the vertebral column (fibres 1–14, respectively).The fine structure of slow (red) fibres (1–2 fibres deep) is relatively homogeneous throughout its range, giving mean values for mitochondria, 21.4%; myofibrils, 61.0%; S.R., 2.10%; T-system, 0.31%. The fibres are relatively small (204 m²) and the mitochondrial cristae poorly developed.In contrast, there is a marked heterogeneity in the ultrastructure of fast (white) fibres, dependent on both position and size. The moderately small (333 m²) superficial fast fibres (3–4 fibres deep) have a significantly higher mitochondrial content (7.6%) than the larger deep fibres (1.2%) (6–12 fibres deep, 775 m²). The mean fractional volumes occupied by myofibrils, S.R., and T-system in the deep fibres are: 80.4%, 5.95%, and 0.38%, respectively. Fibres < 100 m² constitute up to 5% of the fast muscle and have a significantly higher mitochondrial volume (4.3%), more glycogen granules, and a slightly lower volume of S.R. (5.57%) than larger fibres.It is suggested that metabolic subpopulations of fast fibres correspond to different stages of fibre growth. The relatively poorly developed S.R. of eel fast muscle is thought to be correlated with the low frequency, high amplitude nature of the propagated waveform found in anguilliform locomotion.     

Purification and phosphorylation of initiation factor eIF-2 from rabbit skeletal muscle

Core particle DNA unfolding and refolding are followed by stopped-flow circular dichroism technique. When core particles are dissociated in the stopped-flow cuvette, the high CD deviation corresponding to the dissociated state is reached in the first millisecond, which means that the dissociation process is completed within the dead time of the apparatus which is ～1 ms. The same conclusion can be drawn when core particles are reassociated, since the low CD value, typical of the associated state, is immediately reached. Similarly histone release from chromatin is a very fast process. We also include some points of discussion about core particle assembly process.     

Identification of putative calcium channels in skeletal muscle microsomes

Saturable binding sites for the labelled calcium antagonist (+/-)[3H]nimodipine were found in guinea-pig hind limb skeletal muscle homogenates. Binding sites were enriched in a microsomal pellet by differential centrifugation of the homogenate. [3H]Nimodipine binding (Kd = 1.5 +/- 0.03 nM, Bmax = 2.1 +/- 0.25 pmol/protein, at 37 degrees C) copurified (6-fold) in this fraction with [3H]ouabain binding (6.6-fold) and 125I-alpha-bungarotoxin binding (5-fold). d-cis-Diltiazem (but not 1-cis-diltiazem) stimulated (+/-) [3H]nimodipine binding (ED50 1 microM) by increasing the Bmax. Binding sites discriminated between the optical enantiomers of 1.4-dihydropyridine calcium antagonists and the optically pure enantiomers of D-600. The data confirm, with biochemical techniques, the presence of 1,4-dihydropyridine and (+/-) D-600 inhibitable calcium channels in skeletal muscle, previously found with electrophysiological techniques.     

Effects of Acute and Chronic Denervation on Release of Acetylcholinesterase and Its Molecular Forms in Rat Diaphragms

Abstract: Hemidiaphragms were removed from rats at various times after intrathoracic transection of the left phrenic nerve and were incubated in organ baths containing 1.5 ml of oxygenated, buffered physiologic saline solution, with added glucose and bovine serum albumin. After incubation, the acetylcholinesterase (AChE; EC 3.1.1.7) activities of the bath fluid and of the muscle were determined. Innervated left hemidiaphragms were found to release 107 units of AChE over a 3-h period, corresponding to 1.9% of their total AChE activity. Denervation led to a rapid loss of AChE from the muscle coincident with a transient increase in the outpouring of enzyme activity into the bath fluid. Thus, 1 day after nerve transection the left hemidiaphragm contained only 68% of the control amount of AChE activity, but released 140% as much as control. After 3 or 4 days of denervation, the AChE activity of the diaphragm stabilized at 35% of the control value. Release also fell below control by this time, but not as far. One week after denervation the release, 69 units per 3 hr, corresponded to 3.3% of the reduced content of AChE activity in the muscle, indicating that denervation caused an increase in the proportion of AChE released. Sucrose density gradient ultracentrifugation showed that 10S AChE accounted for more than 80% of the released enzyme activity at all times. The results did not rule out the possibility, however, that the released enzyme originally stemmed from 4S or 16S AChE in the diaphragm.     

Biochemical changes in tissue composition of Periplaneta americana (Linn.) acclimated to high and low temperatures

1. 1.|Cold acclimation apparently favours an increase of water content in fat body, but not in coxal muscle, of cockroaches.

2. 2.|A remarkable enhancement in the accumulation of total protein in fat body characterizes the cold acclimation of cockroaches, particularly adult males (175% increase in protein/DNA ratio). The increase in protein content of coxal muscle during acclimination to 15°C, observed in nymphs (16%) and males (16%) but not in females, is less pronounced than that of fat body.

3. 3.|A diminution (28–32%) in the free amino acid/DNA ratio due to cold acclimation has been recorded in both coxal muscle and fat body of nymphs and females, but not in males.

4. 4.|No qualitative change occurs in the free amino acid spectrum of haemolymph and tissues of this insect during acclimation to 15 and 35°C.

5. 5.|An augmentation (15–30%) of the RNA/DNA ratio occurs in fat body and coxal muscle of nymphs and males but in fat body alone of females following cold acclimation.

6. 6.|The glycogen reserve has been shown to increase by up to 30% in fat body and coxal muscle of cold acclimated cockroaches compared to warm acclimated ones.

Differentiation of Ca2+ pumps linked to plasma membrane and endoplasmic reticulum in the microsomal fraction from intestinal smooth muscle

ATP promotes ⁴⁵Ca uptake by the microsomal fraction from the longitudinal smooth muscle of guinea-pig ileum and this uptake is stimulated by oxalate. As the microsomal fraction is made up of various subcellular entities, we examined the localization of the Ca²⁺-transport activity by density gradient centrifugation, taking advantage of the selective effect of digitonin (at low concentration) on the density of plasmalemmal elements. When the ⁴⁵Ca-uptake activity was measured in the absence of oxalate, its behavior in subfractionation experiments closely paralleled that of the plasmalemmal marker 5′-nucleotidase. In contrast, the additional Ca²⁺-transport activity elicited by oxalate behaved like NADH-cytochrome $\text{c}$ reductase, a putative endoplasmic reticulum marker. The endoplasmic reticulum vesicles constituted only a small part of the membranes in the microsomal fraction, which explains that their Ca²⁺-storage capacity was not detectable in the absence of Ca²⁺-trapping agent. Low digitonin concentrations selectively increased the Ca²⁺ permeability of the plasmalemmal vesicles. The two Ca²⁺-transport activities were further differentiated by their distinct sensitivities to K⁺, vanadate and calmodulin. In this respect, the oxalte-insensitive and oxalate-stimulated Ca²⁺-transport systems resembled, respectively, the sarcolemmal and sarcoplasmic reticulum Ca²⁺ pumps in cardiac and skeletal muscle, in accordance with the subcellular locations established by density gradient centrifugation.     

The membrane systems in different fibre types of the triceps surae muscle of cat

Summary The volume and surface area of mitochondria and sarcoplasmic reticulum in fast and slow twitch fibres of the cat triceps surae muscle were determined from thin sections. The width of the Z-line and the array of glycogen granules identified fast and slow twitch fibres.The relative volume occupied by mitochondria was largest in slow twitch gastrocnemius fibres. Fast twitch fibres showed the greatest scatter of mitochondrial content. This corresponds with the fact that motor units of the fast twitch type differ most with respect to resistance to fatigue.The relative volume of the sarcoplasmic reticulum was twice as large in fast as in slow twitch fibres. The volume fraction occupied by longitudinal tubules of the reticulum was the same in fast and slow twitch gastrocnemius fibres but was only half as large in the slow twitch soleus fibres. This difference may be related to post-tetanic potentiation: this property is present in all gastrocnemius fibres but is absent in soleus fibres.The specific tetanic force is 3 to 5 times smaller in slow twitch gastrocnemius than in slow twitch soleus fibres or fast gastrocnemius fibres. There was, however, no detectable morphological difference that might be related to this difference in force.Freeze fractures demonstrated directly that, in soleus fibres, terminal cisternae and longitudinal tubules of the reticulum were scarce as compared to gastrocnemius fibres. The plasma membranes of some gastrocnemius fibres displayed square arrays of 60-nm particles; these arrays were absent in other gastrocnemius fibres and in all soleus fibres. They probably characterize plasma membranes of fast twitch fibres.This study was supported by grants from the Danish Medical Research Council. I wish to thank Mrs. M. Bjærg for valuable technical help