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Biomedical subjects

A SANDOW

Publications and source records attributed to A SANDOW.

At least 19 recordsLinked to original sources
PubMed1964

MUSCULAR CONTRACTION AS REGULATED BY THE ACTION POTENTIAL.

Lowering the mechanical threshold and, independently, prolonging the duration of the action potential cause an increased rate of tension development, as well as potentiation of the twitch, of frog skeletal muscle. The alterations of the two different features of function of the action potential modify excitation-contraction coupling in essentially identical fashion (probably by increasing the liberation of free Ca(2+) into the myoplasm), and this results in early intensification as well as later prolongation of the active state.

Action Potentials↗
PubMed1964

ELECTROCHEMICAL COUPLING IN POTENTIATION OF MUSCULAR CONTRACTION.

Diverse potentiators of contraction have basically identical, activestate mechanical effects, but act by different membrane-mediated electromechanical coupling mechanisms. The falling phase of the action potential is greatly prolonged by Zn(2+) (0.1 mM) and UO(2)(2+) (0.5 to 1 microM), neither of which affects the mechanical threshold. Caffeine (1 mM), like the lyotropic anions, acts conversely. Thus changes in the duration and mechanical threshold of the action potential determine independent electromechanical coupling processes which can act individually, or conjointly in the action of other potentiators, in determining the duration of the active state and thus the potentiation of twitch tension.

Action Potentials↗
PubMed1963

Effects of zinc on responses of skeletal muscle.

Zn(++) potentiates the twitch tension of the frog's sartorius muscle by as much as two to three times, and prolongs twitch time parameters. Tetanus tension is unchanged, but fusion frequency is reduced. Thus, the basic mechanical effect of Zn(++) is prolongation, but not intensification, of the active state. Threshold effects appear at about 0.005 mM Zn(++), and maximal changes at 0.05 mM. In 0.05 mM, potentiation begins after a delay of about 1 min. and develops with half-time of 6 min.; full changes reverse in pure Ringer's with halftime of 60 min. Diffusion theory analysis of these kinetics indicates that the potentiating action of zinc involves special features not found in potentiation by anions: a primary membrane action is not excluded, but Zn(++) may have to penetrate to and act at sarcoplasmic reticular or myoplasmic sites. Zn(++) does induce excitatory membrane effects: the fall of the action potential is slowed and the refractory period is increased about four times; but excitability as such is not changed. Unique chemical features of Zn(++) are discussed in relation to possible mechanisms of its action on muscle fibers.

Action Potentials↗
PubMed1961

Fatigue in phasic and tonic fibers of frog muscle.

Single isolated phasic muscle fibers and small bundles of tonic fibers were directly stimulated in one-per-second twitch series by massive electrode shocks. During the stimulation period the isometric tension developed by the phasic fiber continuously decreased, first rapidly and then slowly. The tonic fibers behaved similarly, but showed much less fatigue than the phasic ones. In general, recovery of the fibers after cessation of stimulation also occurred in two phases.

Animals↗
PubMed1959

Active state of muscle in iodoacetate rigor.

Frog sartorius muscles, equilibrated to 2 x 10(-4)M iodoacetic acid-Ringer's solution and activated by a series of twitches or a long tetanus, perform a rigor response consisting in general of a contractile change which plateaus and is then automatically reversed. Isotonic rigor shortening obeys a force-velocity relation which, with certain differences in value of the constants, accords with Hill's equation for this relation. Changes in rigidity during either isotonic or isometric rigor response show that the capacity of the rigor muscle to bear a load increases more abruptly than the corresponding onset of the ordinarily recorded response, briefly plateaus, and then decays. A quick release of about 1 mm. applied at any instant of isometric rigor output causes the tension to drop instantaneously to zero and then redevelop, the rate of redevelopment varying as does the intensity of the load-bearing capacity. These results demonstrate that rigor mechanical responses result from interaction of a passive, undamped series elastic component, and a contractile component with active state properties like those of normal contraction. Adenosinetriphosphate is known to break down in association with development of the rigor active state. This is discussed in relation to the apparent absence of ATP splitting in normal activation of the contractile component.

Adenosine Triphosphate↗