Wallace O. Fenn

A quantitative comparison between the energy liberated and the work performed by the isolated sartorius muscle of the frog

THIS work is the result of a suggestion by Prof. A. V. Hill that the heat production of muscles allowed to shorten and do work should be reinvestigated by means of the improved myothermal methods which he and Hartree(l) have developed and have applied with such success to muscles in isometric contraction. As shown by their work on the difficult problem of the thermo-elastic effect(2), this technique makes it possible to allow muscles to shorten without errors due to slipping over the junctions provided strict precautions be taken to insure uniformity of temperature. The primary object of the experiments was to measure the maximum efficiency attainable with a frogs muscle under ideal conditions of load, etc. This has been done and the result shows an astonishingly low efficiency. The experiments, moreover, have led to important modifications of some of the fundamental and accepted principles of muscle physiology. In particular it can now be shown that there is a fairly good quantitative relation between the heat production of muscles and the work which they perform, and that a muscle which does work liberates, ipsofacto, an extra supply of energy which does not appear in an isometric contraction. Having reached this rather novel point of view, it was a surprise to find that in its essentials it was not new but was urged by A. Fick 30 years ago, without, however, a satisfactory experimental basis. For this reason the history of the subject is of interest. Heidenhain(3) first showed that if increasing weights were hung on a muscle (not after-loaded) then the heat production caused by the contraction of the muscie and the lifting of the weight increased with increase in the weight. Both Fick(4) and Heidenhain(3) added to this fact the observation that the heat also increased with the load even if the muscle always contracted from the same initial position. This was accomplished either by after-loading the muscle or by the use of Ficks

Muscular force at different speeds of shortening

IN a study of the mechanics of human muscle Hill [1922] came to the conclusion that a muscle could be represented mechanically by a spring working in a viscous medium. As the speed of shortening (v) of the muscle increased he found that the work done or the tension exerted (W) fell off linearly according to the equation W= WOkv. Although the equation represented the experiments very satisfactorily it should be mentioned that the observations may have been complicated by reflex changes in the degree of innervation of the muscles in the supposedly maximal voluntary contractions (though Lupton [1922] with a quickrelease mechanism obtained the same result). Moreover, the experiments of Gasser and Hill [1924] on isolated frog muscles showed that this simple linear relation did not generally obtain under these conditions. These experiments were followed by some observations of Levin and Wyman [1927] on the relation between the force and the speed of shortening or the speed of stretching of muscles of dogfish and other animals. The expected linear relation between force and speed was not found and the authors concluded that the muscle represented a system of two components, an undamped elasticity and a damped elasticity, the latter behaving according to the equation suggested by Hill. When the muscle was suddenly released the undamped system could shorten instantaneously and could keep the tension from falling rapidly as it otherwise would. This two-component system has been widely used by subsequent workers [Bouckaert, Capellen and de Blende, 1930; Mayer and Bouckaert, 1932; Petit, 1931; Sulzer, 1928]. The work of Bouckaert, Capellen and de Blende [1930] is of special interest in this connection. They arranged to measure the rate of

The relation between the work performed and the energy liberated in muscular contraction

MEASUREMENTS by Hartree and A. V. Hill(i) of the initial heat production of the sartorius muscle of the frog arranged to contract isometrically have shown that the total energy so liberated, I, is equal to A, the energy necessary to set up the tension, plus Bt, the energy necessary to maintain it for the duration of the contraction. Thus: I=A+Bt ...... (1). In a previous paper (2) based upon similar measurements of the initial heat produced when the muscle is allowed to shorten during stimulation, I have shown that when work is done by the muscle an extra supply of energy is liberated which does not appear in an isometric contraction and which is roughly proportional to the work, W, which is done. Thus the total energy, E, liberated is given by the formula: E =A+ Bt +kTs= I+kW ...... (2), where T is the tension of the muscle during shortening and s is the amount of shortening. It is the purpose of this paper to discuss the significance of the term kW, particularly from the point of view of the theory that a stimulated muscle can be regarded as an elastic body, and to present further experiments which make possible a more detailed analysis of the excess energy, kW.

Mechanics of respiration

Abstract This outline of the mechanics of breathing is not altogether new and is largely a summary of recent work on the subject from the authors laboratory. The data apply primarily to normal healthy young males and the variations to be expected in other age groups and in clinical practice are still unknown. The outline is unsatisfactory also because of inadequate information concerning the elasticity of the human lung and its proper position on the pressurevolume diagram. No attempt has been made to deal separately with abdominal and thoracic types of breathing and indeed the data for this purpose are non-existent. The distribution of resistance to air flow between the upper and lower respiratory passages is not well documented experimentally and would be of much clinical interest. At best, an outline of the mechanical problems of breathing has been sketched and some possible methods of attack have been suggested for future additions to our knowledge of the subject.

THE BURNING OF CO IN TISSUES

My discovery of the burning of carbon monoxide in tissues, nearly 40 years ago,l* & b came about quite unexpectedly when I tried to measure the inhibition of the oxygen consumption of frog muscle by CO. To my great surprise, rather than an inhibition, there was a very considerable acceleration of oxygen consumption. FIGURE 1 shows a summary of my primary observations with frog muscles. The total observed decrease in volume, as observed by the movements of the index drop in one of my differential volumeters, is calc dated as if it were all oxygen, and this is plotted as ordinates. The abscissae represent percentages of oxygen in mixtures with either nitrogen or CO. The lower curve indicates the results with nitrogen; the rate of oxygen consumption increases to a maximum when the concentration is sufficient to diffuse enough oxygen for the needs of the tissue. When CO is substituted for the nitrogen, the upper curve results. The excess 0 2 observed was maximum at 70% CO and 30% 02. I regarded this result, at first, with great distrust, and tried every possible control experiment. The rate did go to zero in the absence of oxygen. In the absence of tissue there was no significant disappearance of CO as formate in the alkali. With nerve and skin in place of muscle, nostimulation by CO was observed. The muscles were not stimulated by the CO to contract and they were not fatigued in any way. I finally adopted the hypothesis that this increase was due to the burning of the CO to carbon dioxide, probably via cytochrome oxidase. Before giving definite proof of this hypothesis, let me say that it occurred to me that the difference between these two curves must represent the rate of the reaction 2 c o + 0 2 = 2 c 0 2

The pH Of muscle

SummaryFrog muscle in the body is in equilibrium with plasma which contains 2.6 times as much bicarbonate. After allowing for the bicarbonate contained in the tissue spaces, a pH of 6.9 for the interior of the fibres is calculated by theHenderson-Hasselbalch equation, while the outside of the fibres is bathed in a solution of pH 7.34.A micromethod is described for extracting from muscles minute quantities of extracellular fluid which is shown to be alkaline in reaction (pH 7.4). Fluid obtained from a site of injury is acid (pH 6.27) and this acidity persists to a lesser degree (pH 7.07) even after lactic acid production has been stopped by iodoacetic acid, which indicates intracellular acidity.When muscles are brought into equilibrium withRingers solution this wide difference in pH between the inside and the outside of the fibres tends to disappear, but some small excess outside remains even after 5 hours except in the most acid solutions. In alkaline solutions the muscle tends to gain bicarbonate and this takes place to some extent even when the muscle is immersed after dissection in blood of the same frog.

Carbon dioxide and intracellular homeostasis.

I have been interested in electrolytes for a long time; my first paper on the subject was published from the laboratory of W. J. V. Osterhout in 1916, who should be remembered as the man who first proposed a carrier mechanism for the active transport of potassium. Later, during World War I, it was my privilege to work for a time in L. J. Henderson’s laboratory, to which I had been assigned as a United States Army sergeant. I t was easy to recognize the greatness of the man although at the time I knew too little about electrolytes and blood to have any real concept of the magnitude of his contributions to science. This appreciation came after I had the opportunity of studying his book on blood and learned that this was one of the most beautifully complete chapters in all of physiology. At that time a few sophisticated persons could talk about pH, and more knew something about hydrogen ion concentrations, which were still measured by a few experts with a potentiometer and a hydrogen electrode. Electrolytes were of interest to a few specialists only and were of no concern to clinicians in general. I t was Henderson who first clearly recognized the remarkable properties of carbonic acid; the Henderson-Hasselbalch equation (by which we calculate pH) still bears his name. He wrote a book called The Fitness of the Environment that included a discussion of the fitness of C02 for biological purposes. Carbonic acid is a weak acid and is easily displaced from base by the addition of a stronger acid, thus providing a large fraction of the buffering of the body. With this auspicious initiation into the subject of electrolytes I could hardly fail to maintain an interest in this field throughout my active career. This paper is something of a review of my long relation to the subject of tissue buffering. One of the best measures of the buffering capacity of blood or tissues is the COZ dissociation curve, which might be regarded as the result of titrating the solution or tissues with carbonic acid. As the COZ tension is increased, base is taken away from the other buffers and becomes available for combining, with bicarbonate. Carbon dioxide is always available to combine with any free base, and the bicarbonate content of a solution or a tissue may be regarded as a measure of the excess of fixed or nonvolatile cations over anions. The COz dissociation curve of blood is well known, but that of tissues is less familiar; therefore, I may well begin a review of tissue buffering a t this point. In so far as I know, the first C02 dissociation curves of tissues were those I described in 19280, which I had investigated with the aid of a somewhat antiquated method (FIGURE 1). The tissue to be analyzed was quickly introduced into the apparatus and subjected to grinding under acid. The COZ released was carried over to Ba(OH)r, where i t was absorbed and analyzed by the electrical conductivity of the medium. These C O Z dissociation curves show that the curve for blood is much higher than that for muscle or nerve. Similar results were obtained by Stella (1929). The curve for heart muscle was even lower than the curve for skeletal muscle

INFLUENCE OF X-IRRADIATION ON OXYGEN POISONING IN MICE

Summary The survival time of mice in 6 atmospheres of oxygen was about 40 minutes. The average survival times were prolonged 12, 22, 34, and 146 minutes, respectively, when the mice were irradiated (8800 r) 30, 48, 72 and 84 hours previously. Anorexia may have contributed to the observed protection.

Interactions of oxygen and inert gases in Drosopfflla

Abstract The narcotic potency for Drosophila of nitrogen (34 atm), argon (24 atm), xenon (1.7 atm), nitrous oxide (1.7 atm) and CO 2 (0.2 atm) is markedly enhanced by raising the oxygen pressure from 0.21 to 1.0 atm or more. In 1 atm of oxygen alone the flies survive about a week, but in the presence of these inert gases this tension of oxygen causes collapse in a few hours. No such synergism between oxygen and inert gases is evident with helium at similar pressures. Alcohol and ether give somewhat similar results; they shorten the survival times at all tensions of oxygen, the optimum partial pressure of oxygen for survival being displaced to values higher than in normal air.

INERT GAS NARCOSIS

The phenomenon of nitrogen narcosis or narcosis by inert gases was originally discovered in laboratory experiments by Meyer and Hopff in 1923. A frog or some other animal was placed in a chamber in air at 1 atm., to which nitrogen or some other inert gas was added, until the frog, observed through windows, was found to be narcotized, as indicated by loss of righting reflexes. The result was found proportional roughly to the solubility of the gases in lipoid. This classical observation has been amply confirmed in the last 40 years, and the general picture has not been changed very much. Some 20 years later, similar observations were made in Russia on mice by Lazarev (1941), and on cats by Orbelli and colleagues (1944). Meanwhile, Hill and Phillips (1932), in British naval operations, had noticed a “slowing of the process of cerebration” which occurred in divers at 300-ft. depth ( 1932). This was confirmed by Behnke and associates in 1935, who showed that the effect must be due to the high concentration of nitrogen. Shilling and Willgrube ( 1937) also studied this effect which came on at once, and did not increase with time. Behnke and Yarborough (1939) extended these observations to the use of argon and helium, while Case and Haldane (1941) added valuable confirmatory evidence. In spite of all this evidence, it seemed important to establish the fact of nitrogen narcosis in some convenient laboratory situation where it could be studied in more detail. With this in mind, Charlotte Haywood, of Mt. Holyoke College, in my laboratory, studied a variety of physiological preparations, including muscle contraction, injury current of muscle, phagocytosis, and locomotion of Daphniu, but even at 60 atm. pressure, she failed to find any measurable effects (unpublished). Later, at Woods Hole., she failed to find any effect of high pressures of nitrogen on the development of sea urchin eggs (1953). She was followed in our laboratory by Jean Marshall, who did succeed in showing that in frogs such pressures of nitrogen would abolish brain waves and reflex activity in the cord. Argon was found more effective in this respect than nitrogen, and helium controls showed no effect. She also added the significant fact that nitrogen narcosis was intensified by small concentrations of COP. In this respect, nitrogen narcosis resembles oxygen poisoning. Many years later, similar experiments were done by Chun (1959) in Russia, using cats. In this case, records were made of the contraction of a semitendinosus muscle stimulated by its motor nerve, and also a record of the inhibition of this contraction caused by contralateral stimulation. When the cat was exposed to 3.8 per cent oxygen in nitrogen at a total pressure ot 7 to 9 atm., the high pressure of nitrogen diminished the response of the muscle almost to nothing in a few minutes, while the inhibitory effect practically disappeared after a lag of only one minute. This constituted a very dramatic demonstration of a narcotic effect of nitrogen, and at a somewhat lower pressure than that found necessary by other investigators. Apparently, the results were not always as striking as this, and