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Biomedical subjects

S Winegrad

Publications and source records attributed to S Winegrad.

68 records · Page 4Linked to original sources
PubMed1976

Spontaneous mechanical activity in depolarized frog ventricle.

Spontaneous mechanical activity can be produced in depolarized frog ventricle by bathing the tissue in a solution with low Na, Iow Ca, and high K+. The contractions can be inhibited by depleting the tissue of Ca first, but they are relatively insensitive to changes in either extracellular [Ca++] or [Ca++]/[Na+]2. They are terminated very rapidly by raising [Na+] to 40 mM. Local anesthetics enhance the spontaneous activity in proportion to the concentration of their free base form. These contractions occur relatively rhythmically for several hours. Since the preparation is multicellular, this suggests a mechanism for intercellular communication without change in membrane potential.

Animals↗
PubMed1976

Effect of muscle length on 45Ca efflux in resting and contracting skeletal muscle.

The increment of the slow component of 45Ca efflux from frog skeletal muscle that is produced by electrical stimulation is reduced by 70% when the muscle has been stretched to 160% of in vivo length. No change in the efflux from resting muscles or the increment in influx associated with stimulation was produced by increased length. The increased efflux produced by 8 mM caffeine was not altered by increased muscle length. Resting and action potentials were unchanged by the stretching. No morphological changes were seen in the transverse tubules or their junction with the terminal cisternae even at sarcomere lengths of 3.8 muM, but the terminal cisternae themselves were elongated at this length.

Action Potentials↗
PubMed1974

Resting sarcomere length-tension relation in living frog heart.

The sarcomere pattern and tension of isolated resting frog atrial trabeculae were continuously monitored. In the absence of any resting tension the sarcomere lengths varied with the diameter of the trabeculae. In over 75 % of the trabeculae the value exceeded 2.05 microm, the estimated in vivo length of the thin filaments, and it was never less than 1.89 microm. When the trabeculae were stretched the increase in length of the central undamaged portion could be completely accounted for by an increase in sarcomere length. The width of the A band was constant only at sarcomere lengths between 2.3 and 2.6 microm it decreased at smaller and increased at larger sarcomere lengths. A group of spontaneously active cells stretched the sarcomeres in cells in series to longer lengths than could be produced by passive tension applied to the ends of the trabeculae, but they did not influence the sarcomeres of adjacent cells. It is proposed that the connective tissue is a major factor in determining sarcomere length and that there are interactions between thick and thin filaments in resting muscles.

Animals↗
PubMed1973

Intracellular calcium binding and release in frog heart.

The capacities and affinities of intracellular calcium-binding sites have been studied in frog ventricles, in which the concentration of Ca(++) in the sarcoplasm can be controlled as a result of treatment with EDTA. The total calcium content of calcium-depleted and nondepleted muscles at rest and muscles generating considerable tension was 0.8, 1.4, and 5.4 micromol/g of muscle, respectively. Net movement of calcium into or out of the cells occurred without change in tension when the sarcoplasmic concentration of Ca(++) was either of two values, less than 10(-7) M or approximately 5 x 10(-7) M. These data can be explained by the presence of two groups of intracellular calcium sinks which compete with the contractile proteins, one with a capacity of about 0.6 micromol/g and an affinity constant greater than 10(7) M(-1) and a second with a capacity of 4.0 micromol/g and an affinity constant of about 2 x 10(6) M(-1). The higher affinity calcium is released by anoxia, oligomycin, or abrupt changes in sarcoplasmic Ca(++). Muscles soaked in Sr-Ringer's contain electron densities in the sarcoplasmic reticulum and to a lesser extent in the mitochondria.

Adenosine Triphosphate↗
PubMed1971

Studies of cardiac muscle with a high permeability to calcium produced by treatment with ethylenediaminetetraacetic acid.

Thin strips of frog ventricle were isolated and bathed for 15 min in a solution containing 140 mM KCl, 5 mM Na(2)ATP, 3 mM EDTA, and 10 mM Tris buffer at pH 7.0. The muscle was then exposed to contracture solutions containing 140 mM KCl, 5 mM Na(2)ATP, 1 mM MgCl(2), 10 mM Tris, 3 mM EGTA, and CaCl(2) in amounts to produce concentrations of free calcium from 10(-4.8)M to 10(-9)M. The muscles developed some tension at approximately 10(-8)M, and maximum tension was achieved in 10(-5)M Ca(++). They relaxed in Ca(++) concentrations less than 10(-8)M. The development of tension by the EDTA-treated muscles was normalized by comparison with twitch tension at a stimulation rate of 9 per min before exposure to EDTA. In 10(-5)M Ca(++) tension was always several times the twitch tension and was greater than the contracture tension of a frog ventricular strip in KCl low Na-Ringer. Tension equal to half-maximum was produced at approximately 10(-6.2)M Ca(++). Intracellular recording of membrane potential indicated that after EDTA treatment the resting potential of cells in Ringer solution with 10(-5)M Ca or less was between 5 and 20 mv. Contracture solutions did not produce tension without prior treatment with EDTA. The high permeability of the membrane produced by EDTA was reversed and the normal resting and action potentials restored in 1 mM Ca-Ringer. Similar studies of EDTA-treated rabbit right ventricular papillary muscle produced a similar tension vs. Ca(++) concentration relation, and the high permeability state reversed with exposure to normal Krebs solution.

Animals↗
PubMed1970

The intracellular site of calcium activaton of contraction in frog skeletal muscle.

Radioautography has been used to localize (45)Ca in isotopically labeled frog skeletal muscle fibers which had been quickly frozen during a maintained tetanus, a declining tetanus, or during the period immediately following a tetanus or a contracture. During a tetanus almost all of the myofibrillar (45)Ca is localized in the region of the sarcomere occupied by the thin filaments. The amount varies with the tension being developed by the muscle. The movement of calcium within the reticulum from the tubular portion to the terminal cisternae during the posttetanic period has a half-time of about 9 sec at room temperature and a Q(10) of about 1.7. Repolarization is not necessary for this movement. Evidence is given to support the notion that most calcium efflux from the cell occurs from the terminal cisternae into the transverse tubules.

Animals↗
PubMed1968

Intracellular calcium movements of frog skeletal muscle during recovery from tetanus.

Radioautographs of (45)Ca-labeled frog skeletal muscles have been prepared using freeze-dry and vapor fixation techniques to avoid displacement of the isotope during the preparation of the radioautographs. (45)Ca has been localized in resting muscles exposed to (45)Ca Ringer's for 5 min or 5 hr and in isotopically labeled muscles recovering from tetanic stimulation at room temperature or at 4 degrees C. In muscles soaked at rest for 5 min (45)Ca was present almost exclusively in the terminal cisternae. In all other muscles there were three sites at which the isotope was concentrated: (a) the terminal cisternae, (b) the intermediate cisternae and the longitudinal tubules, and (c) the A band portion of the myofibrils. The terminal cisternae were labeled more rapidly than the myofibrils, but both exchanges were accelerated by electrical stimulation. The amount of (45)Ca in the longitudinal tubules and the intermediate cisternae decreased with time after a tetanus as the amount in the terminal cisternae increased. It is proposed that electrical stimulation releases calcium from the terminal cisternae and that relaxation occurs from the binding of the released calcium by the longitudinal tubules and the intermediate cisternae. Complete recovery from mechanical activity involves the transport of this bound calcium into the reticulum and its subsequent binding by the terminal cisternae. Resting exchange of calcium occurs primarily between the terminal cisternae and the transverse tubules.

Animals↗
PubMed1965

The location of muscle calcium with respect to the myofibrils.

Autoradiographs have been prepared from frog toe muscles soaked in Ca(45) and fixed with an osmium-oxalate solution. A majority of the grains over the A bands were over the myofibrils. The grain density over the I bands was greatest over the space between the myofibrils. The significance of this distribution is discussed in the light of previous information about the longitudinal distribution of Ca(45) in skeletal muscle.

Animals↗