Tsuneo Tomita

Spectral response curves of single cones in the carp

Abstract Single cone spectral response curves were obtained with the aid of specially designed equipment. Statistical analysis of 142 records selected from hundreds, based solely on the greatest signal-to-noise ratio, revealed three groups of cones; the red cones (74 per cent) with the peaking wavelength at 611±23mμ, green cones (10 per cent) at 529±14mμ , and blue cones (16 per cent at 462±15mμ). These peaking wavelengths are in close accord with those of single cone absorption spectra measured by Marks and MacNichol in the goldfish by a microspectrophotometer. Apparently, Youngs trichromatic theory applies at the photoreceptor level in Cyprinidae.

Studies on the mass receptor potential of the isolated frog retina : I. General properties of the response

Abstract By means of fractional depth recording it was established that treatment of the excised frog retina with Ringer solutions containing sodium aspartate resulted in the suppression of the PII and proximal PIII components of the ERG and, therefore, the isolation of the distal PIII or receptor potential. Concentrations of aspartate of 10mM and 110mM were equally effective. The effect of aspartate was reversible, and the preparation was stable for upwards of one hour. Mass responses could thus be recorded using a pair of large external electrodes on the opposite sides of the retina. Using the mass response, the spectral sensitivity, fast and slow phases of the potential, and effects of transretinal current were studied.

Light-induced resistance changes in single photoreceptors ofnecturus andgekko

Abstract Intracellular recordings from single photoreceptors ofNecturus maculosus andGekko gekko reveal that the response to light is a hyperpolarization accompanied by an increase in resistance. Passive hyperpolarization of the membrane by extrinsic current does not change the membrane resistance but makes the hyperpolarizing response to light larger. By applying a depolarizing current, the response is made smaller, or even inverted if the current is strong enough. It is suggested that the vertebrate photoreceptor is depolarized in darkness and repolarized in light. This new viewpoint accounts for the unusual polarity of the ERG component ascribed to the receptors. The electrogenesis of theS potential is also discussed in relation to the receptor potential.

Electrical activity of vertebrate photoreceptors.

It has been known since the time of Schultze (1866) that in the vertebrate retina there are two types of photoreceptors, rods and cones, and that they serve different visual functions; rods for scotopic vision, and cones for photopic. The terminology originates from the shape of the outer segments in which the photosensitive pigment molecules are contained. The cone outer segments are conic and taper towards the tips, while the rod outer segments are typically cylindrical. Fig. 1 is a schematic diagram from Brown, Gibbons & Wald (1963) of the ultrastructure of the rod and cone outer segments of the mudpuppy, Necturus , as studied by electron microscopy. Both appear to be made up of a pile of transverse paired membranes. In cones these arise by infolding of the plasma membrane, and in rods they have probably arisen in a similar way, but each pair of membranes is sealed around the edge so as to form a closed double-membrane disc (Sjostrand, 1961). Because of the universal lamellation within the rod and cone outer segments, it looks as if there were no appreciable intracellular space, but yet Toyoda, Nosaki & Tomita (1969), and Toyoda et al. (1970) were successful in intracellular recording from the outer segments of single rods of the nocturnal gecko and frog.

Studies on the mass receptor potential of the isolated frog retina: II. On the basis of the ionic mechanism

Abstract The receptor potential of the excised frog retina was isolated by treatment of the tissue with Ringer solutions containing sodium aspartate, and was recorded by means of a pair of external electrodes on the opposite sides of the retina. Except at very low concentrations, the amplitude of the receptor potential varied in direct linear proportion to the logarithm of the external sodium concentration, and in inverse linear proportion to the logarithm of the external potassium concentration. The receptor potential could be generated by light even after the metabolic mechanism has been suppressed by ouabain, providing that a sodium concentration gradient was maintained. It was concluded that the primary action of light in generating the receptor potential is one of decreasing the permeability of the photoreceptor membrane to sodium. The metabolic pump is important only in maintaining the normal sodium concentration gradient. A model in the outer segment was proposed to explain the ionic mechanism in terms of the present and previous studies.

Electrical Activity in the Vertebrate Retina

Descriptions are made of recent developments in research on the S potential and the ERG, two major responses in the vertebrate retina which undoubtedly represent important processes that are intermediate between the initial photochemical process and nervous activity as encoded information to the brain. Both of these responses, together with the nervous activity, have played a superb role as tools to the understanding of many psychophysical phenomena in terms of what is actually taking place in the retina. In this paper, however, emphasis is placed on the effort of investigators during the last decade toward the attainment of more basic knowledge concerning these tools themselves. The progress may not have been completely satisfactory, but the question of how the individual cellular units contribute to these responses will doubtless continue to be of interest to investigators.

The rod response in the frog as studied by intracellular recording

Abstract An electrical response (hyperpolarization to light) was recorded intracellularly from rod outer segments in the isolated frog retina. The recording site was confirmed by a marking technique and also by the fact that the spectral sensitivity curve calculated from the spectral response and from the intensity-amplitude relation agrees with the absorption spectrum of the rod pigment. The slow time course of the response, especially its prolongation after light stimuli of high intensities, and the saturation of the response amplitude at relatively low light intensities are characteristic of the rods.

A Compensation Circuit for Coaxial and Double-Barreled Microelectrodes

In both the coaxial and double-barreled micropipet electrodes, capacitative interference occurs across the wall that makes the boundary between the two pipets. Report will be made on a device which compensates this interference as well as the capacitance of each pipet. A combination of vacuum tubes and transistors was found useful.

Morphological and Physiological Identification of Retinal Cells in the Turtle

Our understanding of retinal function has benefited from the introduction of intracellular marking techniques that allow a particular cell to be fully characterized both as to its physiological function and morphology. The Procion yellow intracellular injection technique originally introduced by Stretton and Kravitz (1968) and perfected for use in the retina by Kaneko (1970, 1971a, b, and Chapter 11 of this volume) has proved most useful. We have used this technique to identify several retinal cell types and to investigate the origin of S-potentials in the turtle retina.