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PubMed1972

Pharmacological properties, cholinesterase activity and anatomy of nerve-muscle junctions in vagus-innervated frog sartorius.

1. The pharmacological properties of the nerve-muscle junctions of vagus-innervated frog sartorius muscles were investigated. Vagus-evoked junctional potentials were ten times more sensitive to hexamethonium than were control end-plate potentials from muscles re-innervated with sartorius nerve. Hexamethonium did not affect passive electrical muscle membrane properties or quantal content. The sensitivity of vagus junctions to D-tubocurarine (dTC) did not differ from the controls.2. The amplitude and time course of vagus-evoked junctional potentials were not affected by eserine or neostigmine. Furthermore, histologically detectable acetylcholinesterase activity was not demonstrable at vagus-muscle junctions.3. The ultrastructure of vagus-innervated muscle fibres was normal in appearance indicating that the vagus was capable of structurally maintaining the muscle fibres.4. Junctional contacts were made by varicosities of unmyelinated vagal fibres. Although such varicose vagal fibres ran along the muscle fibres for long distances, they seemed to make synaptic contacts primarily at old end-plate regions, as deduced from persisting junctional folds.5. It is concluded that at least several ;trophic' factors are probably involved in the different effects of the vagus nerve on the sartorius muscle.

Acetylcholinesterase↗
PubMed1982

Chloride activity and its control in skeletal and cardiac muscle.

Ion-selective microelectrodes have been used to compare the mechanisms controlling intracellular Cl- activity in skeletal and cardiac muscle. In frog Sartorius skeletal muscle fibres, Cl- levels are low (about 3 mM) and are determined mainly passively. The effect of any Cl- transport system will be quickly short-circuited through the high membrane Cl- conductance. In contrast, the sheep-heart Purkinje fibre, like other cardiac tissues, contains higher than passive levels of intracellular Cl- (20-30 mM). Many Cl- movements occur, not through Cl- channels (the permeability for Cl- is low), but by a Cl- -HCO3- countertransport system. High internal Cl- levels are achieved by an exchange of extracellular Cl- for intracellular HCO3-, which acidifies the fibre by 0.3 pH. Anion exchange in heart differs from that proposed for other excitable cells in that it is not specialized to compensate for an intracellular acidosis. Instead, it can prevent the fibres from becoming too alkaline by promoting a bicarbonate efflux and a chloride influx whenever internal bicarbonate levels rise. Possible reasons for this are briefly discussed.

Animals↗
PubMed1996

A critical period for the specification of motor pools in the chick lumbosacral spinal cord.

When 3-4 segments of the chick lumbosacral neural tube are reversed in the anterior-posterior axis at stage 15 (embryonic day 2.5), the spinal cord develops with a reversed organization of motoneurons projecting to individual muscles in the limb (C. Lance-Jones and L. Landmesser (1980) J. Physiol. 302, 581-602). This finding indicated that motoneuron precursors or components of their local environment were specified with respect to target by stage 15. To identify the timing of this event, we have now assessed motoneuron projections after equivalent neural tube reversals at earlier stages of development. Lumbosacral neural tube segments 1-3 (+/- one segment cranial or caudal) were reversed in the anterior-posterior axis at stages 13 and 14 (embryonic day 2). The locations of motoneurons innervating two thigh muscles, the sartorius and femorotibialis, were mapped via retrograde horseradish peroxidase labeling at stages 35-36 (embryonic days 9-10). In a sample of embryos, counts were made of the total number of motoneurons in the lateral motor columns of reversed segments. The majority of motoneurons projecting to the sartorius and femorotibialis were in a normal position within the spinal cord. Segmental differences in motor column size were also similar to normal. These observations indicate that positional cues external to the LS neural tube can affect motoneuron commitment and number at stages 13-14. Since these observations stand in contrast to results following stage 15 reversals, we conclude that regional differences related to motoneuron target identity are normally specified or stabilized within the anterior LS neural tube between stages 14 and 15. To examine the role of the notochord in this process, neural tube reversals were performed at stages 13-14 as described above, except that the underlying notochord was also reversed. Projections to the sartorius and femorotibialis muscles did not differ significantly from those in embryos with neural tube reversals alone, indicating that the notochord is not the source of cues for target identity at stages 13-14.

Animals↗
PubMed1982

Effects of hypertonicity on frog muscle contractures induced by quinine.

1. Frog sartorius and extensor longus digiti ("toe") muscles were used to investigate the effects of solutions of two (2T) and three (3T) times normal tonicity on the contractures elicited by quinine or by high-[K]O media, and on twitch and tetanic tension. 2. Solution 2T had no effect on the peak amplitude of quinine-induced contractures (PQ) of toe muscle but increased the PQ of sartorius muscle. Toe muscle PQ was significantly reduced by 3T. The quinine-induced contractures of sartorii bathed in 3T were slower than, but reached peak values not significantly different from, those obtained with control Ringer solution (1T). 3. The twitch and tetanic contractions of both sartorius and toe muscles were partially or totally blocked by 2T and were always abolished by solution 3T. 4. The maximal amplitude of K+-induced contractures (PK) of toe muscle was significantly reduced, but not abolished, by solutions 2T and 3T. The PK of sartorius muscle was greater at 2T than at 1T, but, in contrast to the transient tension recorded for 1T, the K+-induced contracture in solution 2T had a prolonged plateau. 5. The results suggest that hypertonicity affects the contractile apparatus as well as the excitation-contraction coupling process. The enhancement of quinine- and K+-induced contractures is ascribed to inhibitory effects of hypertonicity on Ca2+-sequestration by the sarcoplasmic reticulum.

Action Potentials↗
PubMedDate not supplied

Miniature end-plate potentials in the frog muscle spindle.

Spontaneous miniature end-plate potentials (m.e.p.p.s) were recorded from the intrafusal muscle fibers in the muscle spindles isolated from the frog sartorius and semitendinosus muscles by means of microelectrode (intracellularly) and across a vaseline gap made transversely on the intrafusal bundle (extracellularly). The latter method was available to record simultaneously the m.e.p.p.s and the afferent terminal activities, of which the latter was easily distinguishable from the former by concomitant occurrence with the axonal responses. Simple type spindles in the sartorius muscle have a restricted end-plate region along the intrafusal bundle on either side of the capsule, while complex type spindles in the semitendinosus muscle are innervated by plural regions which are found on both sides of the capsule in most preparations. Application of 2X hypertonic Ringer's solutions with NaCl or sucrose induced an increase in the rate of the m.e.p.p.s preceding a decrease in the rate of afferent discharges from the spindle.

Afferent Pathways↗
PubMedDate not supplied

Treatment of trochanteric ulcers with cranial sartorius and rectus femoris muscle flaps.

Five dogs with pressure ulcers over the greater trochanter were treated by debridement and transposition of the cranial part of the sartorius or the rectus femoris muscle. Both muscles had vascular anatomy that allowed transposition based on a major vascular pedicle. All wounds healed promptly by primary intention and no ulcer recurred. The cranial sartorius flap technique was easier to perform than the rectus femoris technique.

Animals↗
PubMed1975

The relative contributions of the folds and caveolae to the surface membrane of frog skeletal muscle fibres at different sarcomere lengths.

The plasmalemmal area of striated muscle fibres is greater than the apparent surface area (A = circumference x length) because of variable folds and the invaginations of the caveolae and T-tubules. Freeze-fracture replicas of the surface membrane of sartorius and semitendinosus muscles from Rana pipiens have been used to determine the numbers and distribution of folds and caveolae at different sarcomere lengths. (1) The plasmalemma folds are variable in size and shape, but are always oriented perpendicular to the long axis of the fibre. The folds vary with stretch, being more prominent at short sarcomere lengths. The caveolae are elliptical invaginations of the plasmalemma which open to the outside by a narrow "neck" of approximately 20 nm. The caveolar lumen has an average long dimension of 81.6 +/- 11.7 nm and an average short dimension of 66.9 +/- 7.9 nm. The caveolar "necks" only can be seen in freeze-fracture replicas and these are distributed in two circumferential bands on either side of the Z-line, and in longitudinal bands separated by distances of 1-5 mum. In the sartorius muscle, at a sarcomere length of 2.8 mum, there is an average number of thirty-seven caveolae per square micrometer of fibre surface. (2) During passive stretch the opening of folds provides membrane for the necessary increase in surface area up to a sarcomere length of about 3.0 mum. This length is defined as the critical sarcomere length (Sc). The number of caveolae remains constant at all sarcomere lengths less than Sc and thus their "necks" have been used as membrane markers to determine the amount of folding at different sarcomere lengths. The membrane area contained in folds and caveolae is expressed as a fraction of the apparent surface area (A). For example, in the sartorius muscle, at a sarcomere length of 2.4 mum, the membrane area, excluding the T-tubules, is: A + 0.1A (folding) + 0.7A (caveolae) = 1.8A. (3) For stretch beyond Sc membrane is provided by the opening of caveolae. At a sarcomere length of about 8 mum all the caveolae are open and the fibres rupture with further stretch. (4) The relative contributions of folds and caveolae vary with sarcomere length in a way that is consistent with assumptions of constant volume and plasmalemma area. The maintenance of constant plasmalemma area, even after excessive stretch, suggests that the plasmalemma is relatively inelastic in this situation.

Animals↗
PubMed1978

The relationship between the transverse and longitudinal nuclear magnetic resonance relaxation rates of muscle water.

Whole frog sartorius and gastrocnemius muscles were incubated in Ringer's solutions, either unenriched or enriched with H2 17Oor 2D2O. Subsequently, the rates of transverse (1/T2) and of longitudinal (1/T1) nuclear magnetic relaxation were measured for 17O, 2D, and 1H at room temperature and at 8.1 MHz. The ratio (T1/T2) for 17O was measured to be approximately 1.5-2.0, close to the value roughly estimated from the Larmor frequency dependence of 1/T1 alone over the range 4.3-8.1 MHz. On the other hand (T1/T2) for 2D and 1H were both measured to lie in the range 9-11. Insofar as the entire 17O signal was detected, the data indicate the presence of an exchange mechanism between the major fraction of intracellular water and a minor fraction characterized by enhanced rates of relaxation. Possible molecular mechanisms are presented.

Animals↗
PubMed1984

Muscle fiber termination at the tendon in the frog's sartorius: a stereological study.

The force produced within skeletal muscle fibers is transmitted to the bone via a myotendinous junction. This junctional region was examined by light and electron microscopy in the sartorius muscles of three Rana temporaria. The muscle fibers tapered and inserted at an angle of about 25 degrees with the connective tissue fascia near the bone. The composition of the structures within the last 100 microns of the fiber was analyzed morphometrically. The T-system, terminal cisternae, and caveolae were the same as in the central region of the muscle fiber. However, the mitochondrial content was higher and the volume of longitudinal sarcoplasmic reticulum was lower than elsewhere in the fiber. The membrane at the end of the fiber had extensive villiform processes interdigitating with the tendon. The surface area of the membrane around the villiform processes was estimated with point-counting techniques and calculated from the stereological equations appropriate for partially anisotropic structures. The extra membrane involved in the myotendinous junction was about 32 times that of the cross-sectional area of the fiber. Part of this additional membrane contained specialized adherens junctions through which the contractile proteins of the muscle are anchored to collagen. The increased area at the myotendinous junction presumably provides greater mechanical strength than a flat termination. The high values of membrane capacitance and specific resistance measured electrophysiologically at the end of the fiber also can be attributed to the characteristics of the terminal membrane structure.

Animals↗
PubMed1985

[Heavy water inhibition of alkali cation transport across the muscle membrane. II. A comparison of the action of D20 and ouabain on the sodium efflux and rubidium influx in magnesium media].

The action of heavy water and ouabain on sodium effluxes and rubidium influxes has been measured and compared in frog muscles (m. sartorius, R. temporaria). Approximately half of muscle sodium was substituted by lithium by preliminary incubation in mixed sodium-lithium media. The ratio of the ouabain-sensitive parts of rubidium influx and sodium efflux is 7.3:10.5, and that of D2O-sensitive parts of corresponding parameters is 7.5:11.3. A conclusion is made that D2O-effect on the Na, K-ATPase system of muscles under investigation resembles ouabain-effect on sodium effluxes as well as on rubidium influxes.

Animals↗