T. TOMITA
44
evidence that the early RF' is lost by disorientation of the pigment, although the pigment remains. It is probable that the lamellar and rhabdomeric structures in the vertebrate and invertebrate photoreceptors are
related to the pigment orientation.
Since most works on the early RP have been performed in animals
other than the fish, no further description of this potential will be given.
The receptor potential to be discussed below is the late RP.
B. Response of Single Photoreceptors
Because of the extremely high density in population of photoreceptors
in the retina, it is impossible to isolate single receptor responses without
using intracellular micropipette electrodes. For intracellular recording,
it is necessary to select retinas having large rods and/or cones. The carp
has a mixed retina consisting of large cones (10 p across at the cone inner
segment) and very slender rods of only a few microns across which are
difficult to impale by micropipettes. Penetration into single carp cones
has been successful by using pipettes having a tip diameter of less than
0.1 p, and with the aid of a device which jolts the retina at a high acceleration toward a vertically held, slowly advancing micropipette ( Tomita,
1965). Whenever a resting potential is recorded and a response to light
is observed, the jolting is stopped to maintain the intracellular position
of the pipette for further observations. With an electrode marking method
the recording site has been identified as the cone inner segment (Kaneko
and Hashimoto, 1967).
The intracellularly recorded response to light is sustained and graded,
and it is hyperpolarizing irrespective of the wavelengths of stimulating
light. When the spectrum is scanned, the response spectra of single cones
such as shown in Fig. 8 are obtained. The figure illustrates three response
spectra which are maximally sensitive at different wavelengths. Figure 9
is the result of a statistical analysis, showing three average response
spectra along with standard deviation curves. Their peaking wavelengths
shown by histograms in Fig. 10 are close to those of absorption spectra
of single cones measured in the goldfish with a microspectrophotometer
( Marks and MacNichol, 1963; Marks, 1965).
No electrophysiological evidence has been provided to implicate
lateral interaction between adjacent photoreceptors. The response of
single cones is practically the same in size, being independent of the
retinal area illuminated, and when tested with a small light spot the response falls off sharply as the spot moves off the recording site. This suggests that the individual receptors are functionally independent, making a
44
evidence that the early RF' is lost by disorientation of the pigment, although the pigment remains. It is probable that the lamellar and rhabdomeric structures in the vertebrate and invertebrate photoreceptors are
related to the pigment orientation.
Since most works on the early RP have been performed in animals
other than the fish, no further description of this potential will be given.
The receptor potential to be discussed below is the late RP.
B. Response of Single Photoreceptors
Because of the extremely high density in population of photoreceptors
in the retina, it is impossible to isolate single receptor responses without
using intracellular micropipette electrodes. For intracellular recording,
it is necessary to select retinas having large rods and/or cones. The carp
has a mixed retina consisting of large cones (10 p across at the cone inner
segment) and very slender rods of only a few microns across which are
difficult to impale by micropipettes. Penetration into single carp cones
has been successful by using pipettes having a tip diameter of less than
0.1 p, and with the aid of a device which jolts the retina at a high acceleration toward a vertically held, slowly advancing micropipette ( Tomita,
1965). Whenever a resting potential is recorded and a response to light
is observed, the jolting is stopped to maintain the intracellular position
of the pipette for further observations. With an electrode marking method
the recording site has been identified as the cone inner segment (Kaneko
and Hashimoto, 1967).
The intracellularly recorded response to light is sustained and graded,
and it is hyperpolarizing irrespective of the wavelengths of stimulating
light. When the spectrum is scanned, the response spectra of single cones
such as shown in Fig. 8 are obtained. The figure illustrates three response
spectra which are maximally sensitive at different wavelengths. Figure 9
is the result of a statistical analysis, showing three average response
spectra along with standard deviation curves. Their peaking wavelengths
shown by histograms in Fig. 10 are close to those of absorption spectra
of single cones measured in the goldfish with a microspectrophotometer
( Marks and MacNichol, 1963; Marks, 1965).
No electrophysiological evidence has been provided to implicate
lateral interaction between adjacent photoreceptors. The response of
single cones is practically the same in size, being independent of the
retinal area illuminated, and when tested with a small light spot the response falls off sharply as the spot moves off the recording site. This suggests that the individual receptors are functionally independent, making a