SUMMARY

1
Four methods of determining the potential difference across the surface membrane of living cells are described.

2
In a wide range of excitable tissues the resting membrane potential is of the order of 50–100 mV. and the action potential of the order of 80–130 mV.

3
At the height of activity the potential difference across the membrane is reversed by 30–50 mV.

4
The potassium concentration inside most excitable cells is 20–50 times greater than that in the external medium; sodium is 3–15 times more concentrated outside than it is inside, while chloride is 5–50 times more concentrated outside than inside. Isolated fibres lose potassium and gain sodium and chloride ions.

5
Potassium appears to exist as a free ion inside nerve and muscle fibres.

6
The nature of the organic anions which balance the high concentration of potassium inside excitable cells is still largely unknown. In certain cases amino-acids such as aspartic acid are present in high concentrations.

7
The resting membrane behaves as though it were moderately permeable to K+ and Cl- but sparingly permeable to Na+. The absolute magnitude of the resting potential is similar to that calculated from the potassium concentrations if allowance is made for the contributions of chloride and other ions. Movements of K+ and Cl- as determined by radioactive tracers or by chemical methods agree with a quantitative formulation of this hypothesis.

8
It is necessary to suppose that sodium is continuously pumped out of excitable cells by a process which depends on metabolism.

9
Electrical activity is due to a large and specific increase in the permeability to sodium. The reversed potential difference across the active membrane arises from the concentration difference of sodium and varies with the external concentration of sodium in the same manner as the theoretical potential of a sodium electrode.

10
In many cells, conduction of impulses is impossible if the external medium does not contain sodium or lithium ions.

11
The rate of rise of the action potential varies with the concentration of sodium ions in the external medium.

12
Sodium enters a nerve fibre when it is active. The quantity entering 1 cm.2 of membrane during one impulse is of the order of 3 μμmol.

13
Entry of sodium is approximately balanced by the leakage of a corresponding quantity of potassium.

14
It is suggested that sodium enters the nerve fibre during the rising phase of the action potential and that potassium leaves during the falling phase.

15
The permeability changes during the action potential probably consist of a rapid but transient increase in the permeability to sodium and a delayed increase in the permeability to potassium. It is suggested that both permeability changes vary with membrane potential in a graded but reversible manner. This hypothesis is applied to the phenomena of subthreshold activity, accomodation and oscillatory behaviour.

16
In vertebrate myelinated fibres there is much evidence to show that conduction is saltatory; this suggests that sodium entry is confined to the nodes of Ranvier, and that the internodes are depolarized by local circuit action.

17
Provided that nerves are not stimulated at a high rate, recovery heat production is sufficient to account for the metabolic extrusion of sodium after activity.

The ionic basis of electrical activity in nerve and muscle

The long QT syndromes: a critical review, new clinical observations and a unifying hypothesis.

There is evidence suggesting that the onset of electrical activity in nerve and muscle depends on a specific permeability increase of the surface membrane which allows sodium ions to enter the fibre at a high rate (for references, see Hodgkin, 1951). Furthermore, it has been shown for the giant axon of the squid (Hodgkin & Huxley, 1952 a) that the amount by which the sodium permeability increases during activity (or depolarization) depends on the value of the potential difference which had been acting on the surface membrane before the depolarization. The present experiments were undertaken in order to look for a similar effect in mammalian Purkinje fibres. By means of a feedback circuit the 'resting' potential could be chosen at will; its effect was observed on certain features of the action potential which are thought to be indicative ofthe sodium permeability, namely the upstroke velocity and the size of the 'overshoot'.

The effect of the cardiac membrane potential on the rapid availability of the sodium-carrying system

Crustacean muscle has been of special interest to physiologists because its myoneural junctions show the properties of central nervous synapses. The muscles are supplied by excitatory and inhibitory nerve fibres which can be stimulated separately, and whose interaction can be studied at the level of the nerve-muscle junction. As was pointed out in recent reviews (Wiersma, 1941; Katz, 1949), much valuable information has been obtained about the organization of the crustacean nerve-muscle system, but little progress has been made in elucidating the mechanisms by which antagonistic nerve impulses exert their effects on the muscle fibres. As a first step, it seemed necessary to study the properties of crustacean muscle fibres, quite apart from their nerve junctions. Hitherto, most of the elementary properties of the crustacean muscle membrane have remained unexplored, largely because of technical difficulties in obtaining suitable fibre preparations. With the help of intracellular electrodes, this difficulty can be overcome, and in the present work extensive use has been made of this method, for stimulating and recording across the surface membrane of individual muscle fibres. The object of this paper is to present electrical measurements on the crustacean muscle membrane, in particular its resistance and capacity, its resting and action potential, and its electrical reactions in various ionic environments. As was indicated in previous notes (Fatt & Katz, 1951 b, 1952), the electric response of crustacean muscle fibres, and especially its persistence in sodium-free media, differs from that of many other excitable tissues, and the evidence for this will be discussed in detail.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1953.sp004884

The electrical properties of crustacean muscle fibres

Microelectrodes with an external diameter of less than 05p,. penetrate the surface membrane of skeletal muscle fibres without causing appreciable damage and can be used to record the resting potential and action potential (Ling & Gerard, 1949; Nastuk & Hodgkin, 1950). This technique has rapidly been extended to other tissues such as frog heart (Woodbury, Woodbury & Hecht, 1950), myelinated nerve (Woodbury & Woodbury, 1950) and the giant axon of the cuttlefish (Weidmann, 1951 a). The present paper contains an account of similar experiments with a preparation of mammalian cardiac muscle, and is a sequel to the preliminary reports by Coraboeuf & Weidmann (1949a, b) and Draper & Weidmann (1950). Most of the experiments were performed on the 'false tendons' of the dog heart. These are slender bundles of the conductive system which run through the ventricular cavity of birds and mammals. Their muscular component is a syncytium of parallel fibres which in the dog have a diameter of about 30,u. In ungulates where the conductive elements are histologically well differentiated they are known as Purkinje threads (Purkinje strands, Purkinje fibres). In canine and human hearts the conductive fibres are said to differ in no essential histological feature from the fibres of typical cardiac muscle (Glomset & Glomset, 1940). We shall therefore employ the term false tendon to describe the dog preparation in preference to the better known one of Purkinje fibres. The principal results reported here are those concerned with the absolute magnitude of the action potential and resting potential. The effect of sodium concentration has also been examined, and the results support the view that electrical activity is due to a large and specific increase in the membrane permeability to sodium (Hodgkin & Katz, 1949; Hodgkin, Huxley & Katz, 1949).

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/jphysiol.1951.sp004653

Cardiac resting and action potentials recorded with an intracellular electrode

The administration of pituitary adrenocorticotrophic hormone (A.C.T.H.) is followed by a temporary decrease in the amount of ascorbic acid present in the adrenals. Under suitable experimental conditions the degree of depletion of adrenal ascorbic acid is a function of the dose of A.C.T.H. administered. This relationship has beenadapted to the quantitative assay of adrenocorticotrophic activity (Sayers and Sayers, 1946). The present paper is a detailed description and evaluation of the method based upon the results of a number of comparative assays carried out over the past two years. DEVELOPMENTAL STUDIES The adrenocorticotrophic activity of the adenohypophysis is subject to marked change with alterations in the internal or external environment of the organism. For this reason the adrenocorticotrophic activity of materials other than highly purified preparations of A.C.T.H. cannot be assayed in the animal whose hypophysis has not been removed.

The assay of adrenocorticotrophic hormone by the adrenal ascorbic acid-depletion method.

Membrane resting and action potentials of single cardiac muscle fibers of the frog ventricle.

An initial report is made on the electrocardiogram of a single heart muscle cell in vivo The potential variations obtained by electrodes placed on opposite sides of the membrane of a heart muscle fibre are 50 to 100 times as large as those recorded by standard limb leads The observations support the assumption that during activation the cell interior becomes positive with respect to its surrounding (depolarization, followed by polarization reversal) Induced alterations in shape and form of the action current of a single heart muscle fiber should provide further insight into the nature of the normal and abnormal electrocardiogram

Membrane Resting and Action Potentials of Single Cardiac Muscle Fibers

Using microelectrodes having an external diameter of less than 1 , µ, potential variations of single cardiac fibers were obtained from frog ventricular muscle in situ. The normal membrane potential consists of a rapid depolarization and slow recovery, the latter occurring in three distinct phases. Digitalis glycosides alter profoundly the slopes of these various phases and drastically shorten the entire period of recovery. The characteristic cardiac action potential is thus converted into a spike which resembles the electrical events recorded for skeletal muscle or nerve. These changes occur independently of mechanical systole which remains essentially unaltered. The deformation of the action potential occurs uniformly throughout the ventricular muscle. They are related to the RS-T segment depression of the surface electrocardiogram which in this instance cannot be explained as being caused by a failure of the diastolic repolarization of the endocardial surface but must be an expression of uniform shortening of the entire process of recovery.

Effects of cardiac glycosides upon the electrical activity of single ventricular fibers of the frog heart, and their relation to the digitalis effect of the electrocardiogram.

Male rats weighing 100 g were injected with vehicle (control group), 0.4 or 4.0 mg/kg/day of ethane-1-hydroxy-1,1-diphosphonate (EHDP). Beginning after 6 days of EHDP treatment all rats received six subcutaneous injections of 3H-thymidine at 8 h intervals. The multiple labeling index of autoradiographically defined labeled cells was determined for the osteoprogenitor cells of the primary spongiosa of the proximal tibial metaphysis. The osteoclasts in the proximal tibial metaphisis were assayed for population parameters and incorporation of labeled nuclei at sequential intervals after the administration of 3H-thymidine. After 6 days of EHDP pre-treatment the multiple labeling index of the osteoprogenitor cells was reduced with 4.0 mg/kg/day dose of EHDP. At the beginning of the experimental kinetic sampling period, after the 6 days of EHDP pre-treatment, EHDP treatment resulted in significant increases in the numbers of osteoclasts, nuclei per osteoclast profile, and total osteoclast nuclei. During the sampling period, the 4.0 mg/kg/day dose of EHDP caused further increases in the number of total osteoclasts. EHDP treatment caused a marked increase in the rate of incorporation and accumulation of 3H-thymidine-labeled nuclei in osteoclasts. Thus, EHDP causes an accelerated rate of osteoclast production from percursor cells in spite of its ability to slow bone resorption. Although the origin of osteoclast nuclei is not clear, the kinetic data from this study suggests that osteoclast nuclei are not arising from osteoprogenitor cells or osteocytes in the EHDP-treated animals.

Lowell A. Woodbury

Papers

The assay of adrenocorticotrophic hormone by the adrenal ascorbic acid-depletion method.

Membrane resting and action potentials of single cardiac muscle fibers of the frog ventricle.

Membrane Resting and Action Potentials of Single Cardiac Muscle Fibers

Effects of cardiac glycosides upon the electrical activity of single ventricular fibers of the frog heart, and their relation to the digitalis effect of the electrocardiogram.

Ethane-1-hydroxy-1, 1-diphosphonate (EHDP) effects on incorporation and accumulation of osteoclast nuclei