J. Leyden Webb

Metabolic Aspects of the Relationship Between the Contractility and Membrane Potentials of the Rat Atrium

Some of the relationships between metabolism, membrane potentials and contractility in cardiac tissue have emerged from a study of the effects of anoxia, depletion of substrate and dinitrophenol on the rat atrium. The repolarization phase of the action potential was shown to be particularly sensitive to disturbances in metabolism. Depression of metabolism resulted in a more rapid repolarization, which may provisionally be interpreted as an acceleration of K+ efflux; restoration of metabolism reversed this effect. A concept relating membrane potentials and metabolism is presented, involving the presence of bound ATP within the membrane.

Cellular Membrane Potentials and Contractility of Normal Rat Atrium and the Effects of Temperature, Tension and Stimulus Frequency

Simultaneous recording of membrane potentials and contractility in isolated rat atria by means of intracellular micro-electrodes and a sensitive strain gage has been used to establish the normal characteristics of the tissue as well as effects of temperature, stimulus frequency and initial tension on muscle. Preliminary correlations between duration of the action potential and the degree of contraction indicate that the rate of repolarization is of major importance in determination of the contractile response.

The Action of Acetylcholine and Epinephrine on the Cellular Membrane Potentials and Contractility of Rat Atrium

Acetylcholine diminished the developed tension of contraction in rat atria; simultaneously there was a slight increase in resting potential, no appreciable change in action potential, a decrease in the rate of conduction, only a minor alteration of the form of contraction, and, most strikingly, a decrease in the duration of the action potential or the area enclosed by it. The rate of repolarization subsequent to the action potential was markedly accelerated. Epinephrine, in general, produced the opposite effects and slowed the repolarization rate as it augmented atrial contraction. Cholinesterase does not seem to play a direct role in cardiac membrane potentials or ion transfer since physostigmine had no effect of its own on the electric manifestations. Certain aspects of the mechanisms involved are discussed.

Acceleration of Rate of the Early Chick Embryo Heart by Visible Light

IN the course of an investigation of the control of the heart rate in the early chick embryo it was noted that under certain conditions exposure to visible light accelerates the rate. The following report presents a study of this phenomenon. There are many reports in the older literature of effects of visible light, unrelated to ultraviolet radiation, on cellular activity. Cessation of amoeboid activity when Pelomyxa was suddenly exposed to light was noted in 18791, and has been extensively studied more recently2,3. Activity of cells in tissue culture is affected by exposure to light; amoeboid activity of lymphocytes in frog spleen explants4, and the rate of beat5 of explants of 6 day chick embryo hearts and of cilia of explants of frog throat epithelium, are all modified by growth of the cultures in visible light. Recently, there have been reports of increased metabolic activity6 and of accelerated growth rate and early hatching7,8 in chick embryos from eggs incubated in permanent light. The stimulation of the chick embryo heart rate to be reported here was obtained in the visible range without addition of dye or photosensitizing agents.

Pharmacologic aspects of monoamine oxidase inhibition.

Abstract The block of an enzyme, such as monoamine oxidase, may be simple but the effect of this block upon the tissue functions are clearly complex. The behavior of intracellular multienzyme systems is difficult to express kinetically and, in addition, the quantitative relationship between the tissue function and the concentration of an intermediate is generally unknown. In the present case the situation is complicated by the presence of multiple pathways: there are several pathways of amine formation, there are an unknown number of amines formed and there are different pathways for the elimination of these amines. This field of investigation is one that particularly requires the simultaneous application of biochemical, physiologic and pharmacologie concepts at the most fundamental levels.