Alexander Sandow

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 Zn2+ (0.1 mM) and UO22+ (0.5 to 1 �M), 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.

LATENCY RELAXATION AND A THEORY OF MUSCULAR MECHANO‐CHEMICAL COUPLING

The purpose of this paper, broadly speaking, is two-fold. First, there will be discussed certain aspects of the latency relaxation (LR), the minute pre-contractile elongation of a stimulated muscle that occurs in the latter half of the latent period, a phenomenon first observed by Rauh (1922). Evidence will be presented to show that the latency relaxation is a real lengthening of the muscle’s contractile material that intervenes between the instant of stimulation and the usual shortening or tension development in a contraction. Further, certain studies of the LR will be considered that suggest it is an indication of a process by which myosin is activated for contraction. The second part of this paper will be concerned with a kinetic theory of mechano-chemical coupling which, in part, is based on the particular significance assigned to the LR. The LR was discovered by Rauh in the course of some experiments designed to settle the then almost 70-year-old question as to whether the latent period exists a t all. To forestall criticism that the demonstration of a mechanical latency merely represented an inertial delay in the response of the registering device, Rauh used an extremely sensitive mechano-optical isometric lever system and photographically recorded the mechanical change during only the first few milliseconds of the twitch response of initially tensed frog sartorii and gastrocnemii. To his astonishment, his records not only exhibited a true delay in the onset of tension development, but they also included a transient negative tension change (the LR) during the latter half of the latent period.

INTRODUCTION TO THE CONFERENCE

In welcoming you to this conference, my function is made particularly pleasant by the presence of so many scientific colleagues from abroad. Science, in its essence, is international and, although its local expression may be a product of prevailing social development and need, the exchange of information and the resultant stimulation of new work, which are the life blood of science, transcend national boundaries. With the return to a world of peace, i t is heartening to witness here a step toward the restoration to normal vigor of the pulse of international scientific exchange. On behalf of The New York Academy of Sciences, I therefore warmly welcome to this conference our colleagues from foreign lands: from France, England, China, Belgium, and New Zealand, from Germany, Hungary, Latin America, and Spain; and I express the earnest desire that our deliberations will not only further science, but also help in cementing unbreakably our ties of international amity. The investigation of muscular contraction has, perhaps, no competitor for its preeminent position LLS the crossroads of the many various active disciplines that comprise biology. Here we find studies of structure: gross, microscopic, and especially today, ultramicroscopic ; and of function in its many subdivisions, such as permeability, metabolism in all its chemical and thermodynamic aspects, bioelectricity, secretion-recalling the behavior of the neuromuscular junction, receptor function-as a t the muscle spindle, and, of course, above all functions, because most pertinent and fascinating, contractility itself. Moreover, in all these biological pursuits, a most powerful motivating role is played by the methods of the chemist, the physicist, and the mathematician. There is no doubt that many of these currents of muscle study have richly developed. Yet, generally speaking, there has been among them a provoking lack of integration. These individual lines of research have coursed through their subject, but they have hardly fused into a common t rmd of progress. Striking limited exceptions to this stat,e of affairs come to mind. We have the notable attempt of the Meyerhof-Hill school to connect the chemical and the heat changes, and that of the Fenn-Hill investigations to relate the niechanical and the heat outputs of muscular activity. But these syntheses, important as they

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 Ca2+ into the myoplasm), and this results in early intensification as well as later prolongation of the active state.

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.

Tetanus relaxation. Temperature effects and Arrhenius analysis.

Abstract Time constants (τ) have been accurately measured for the exponentially falling, latter 60–70% of the relaxation phase of maximal isometric tetani of the mouse extensor digitorum longus muscle over the range 15–35°C. Corresponding to the τ values, the rate constants (k = 25.0−189 s-1) are assumed to describe a temperature-sensitive, first-order, rate-limiting reaction underlying, and determining the kinetics of, muscle relaxation. The mean Arrhenius plot for the k values of 6 muscles consists of 2 linear segments with a 25°C transition temperature. The activation energies at the relatively lower and higher temperatures are 22.9 and 12.6 kcal/mol, respectively. These values are qualitatively, and to some extent quantitatively, similar to corresponding known Arrhenius results of the Ca2+ active transport mechanism and the physical properties of the membrane of isolated sarcoplasmic reticulum. Thus, the present findings strongly indicate that relaxation of living muscle critically involves the ‘relaxing factor’ activity of Ca2+ uptake, as previously inferred from research on isolated sarcoplasmic reticulum. Using transition-state theory, the Arrhenius results indicate that ΔG ‡ of the assumed rate-limiting reaction is 14.8–15.0 kcal/mol at all temperatures studied, and ΔS ‡ is about 25 and −10 cal/degree per mol at temperatures below and above the transition temperature, respectively. These also correspond, at least qualitatively, to the values of the activation thermodynamic parameters of isolated sarcoplasmic reticulum. The negative ΔS ‡ at the higher temperature range, denoting an increase in order associated with the assumed activation process of the Ca2+ transport system, requires clarification.

Deuterium oxide effects on excitation-contraction coupling of skeletal muscle.

2H2O (99.8%) Ringers solution greatly reduces the twitch and tetanus of frog sartorius muscle and, as specially shown here, slows the onset features of the mechanical output of the twitch by: (a) increasing the time (LR) from stimulus to start of latency relaxation; (b) slowing the development of the latency relaxation, and (c) greatly decreasing the rate of onset of tension development. These changes reflect effects of 2H2O on excitation-contraction coupling and they represent the critical direct effects of 2H2O on muscle since it does not depress either the action potential or the intrinsic myofibrillar contractility. The increase in LR is attributed to slowed inward electrical propagation in the T-tubule. But the critical effect of 2H2O on frog muscle is to greatly depress mobilization of activator Ca2+. The depression of the Ca2+ mobilization and of its effects on the activation of contraction evidently result from (a) a lowered rate of release of Ca2+ from the sar coplasmic reticulum, as indicated by the slowed development of the latency relaxation, (b) a decreased amount of Ca2+ released in a twitch, and (c) a reduced speed of diffusion of the Ca2+ to the contractile filaments. The depressed mobilization of Ca2+ is apparently the essential cause of 2H2Os general depression of twitch and tetanus output.

The Anti-Bacterial Activity of Egg-White.

The utilization of egg-white as pabulum by bacteria is a fact of common experience. Egg-white also possesses marked anti-bacterial properties for certain bacteria. This phenomena was investigated in the work reported here. Egg-white was removed aseptically from fresh store eggs with a sterile syringe and serially diluted with meat-infusion broth pH 7.5 to 7.6. One cc. quantities of these dilutions were distributed into separate sterile small (Wassermann) test tubes and each tube, including a control tube of broth, was inoculated and well mixed with 0.1 cc. of a 24-hour broth culture of the organisms used. Similar series were made with inocula of 0.1 cc. of a 1-100 and 0.1 cc. of a 1-10,000 dilution in broth of the broth cultures. All tubes were incubated for 20 to 24 hours and then observed for inhibition of growth. In addition, loopfuls of the mixture from each tube were separately streaked out on agar plates (blood agar for streptococcus) which were incubated for 24 hours and then examined for growth. Absence of growth in the streaks on the agar plates was assumed to indicate sterilization of the inocula in the corresponding tubes.

Detubulation effects on the action of zinc on frog skeletal muscle action potential

SummaryDetubulation of the untreated fiber decreases the time constant of the action potentials foot (τf) and increases the maximal rate of rise of the spike (