Toru Kujiraoka

Effect of cadmium on gap junctional intercellular communication in primary cultures of rat renal proximal tubular cells.

Cadmium mainly accumulates in the kidney and causes renal injury. To clarify the mechanism of Cd nephrotoxicity, we investigated the effects of this element on intercellular communication through gap junction channels in primary cultures of rat renal proximal tubular cells. Sixty minutes after exposure to 100 microM Cd, dye coupling experiments showed that gap junctional intercellular communication (GJIC) was significantly inhibited. This inhibition occurred before the appearance of cytotoxicity. Intracellular calcium concentrations [Ca2+]i, which modulate the function of gap junctions, gradually increased after exposure to Cd and reached a maximum after 60 minutes. These results suggest that the inhibition of GJIC as a result of Cd exposure is related to an increase in [Ca2+]i, and that GJIC inhibition may be an indicator of nephrotoxicity.

Color-opponent responses of small and giant bipolar cells in the carp retina

The physiological and morphological properties of color-opponent bipolar cells in the carp retina were studied. Fifty nine OFF-center bipolar cells and 63 ON-center bipolar cells out of about 500 total bipolar cells recorded showed color-opponent responses. The OFF-center color-opponent bipolar cells were classified into three subgroups according to their spectral and spatial responses. Fifty OFF-center color-opponent cells responded with depolarization to a blue light spot and with hyperpolarization to a red spot in the receptive-field center. The polarity of the surround response was opposite to that of center response at each wavelength. Therefore these cells were classified as OFF double-opponent cells (OFF-DO). Eight cells responded with hyperpolarization to a blue and green spot and with depolarization to a red spot. The surround responses of those cells were depolarizing at any wavelength (R+G- cell). One responded with hyperpolarization to a blue and red spot and with depolarization to a green spot. The surround response showed a different spectral characteristic from that of the center response. It responded with depolarization to a blue and green annulus and with hyperpolarization to a red annulus (R-G+B- cell). The ON-center color-opponent bipolar cells were similarly classified into three subgroups. Sixty of ON-center color-opponent cells were the double color-opponent type (ON-DO cell), showing the responses of opposite polarity to the OFF-DO cells. Two cells were classified as R- G+ cell, and one cell as R+G-B+ cell. Both OFF- and ON-DO cells were identified by their morphology as Cajals giant bipolar cells, and R+G-, R-G+, R-G+B-, and R+G-B+ cells as Cajals small bipolar cells. The analysis of the latency and the ionic mechanisms of their responses suggest that DO cells under light-adapted conditions receive direct inputs from long-wavelength (red) cones, RG cells from middle-wavelength (green) cones, and RGB cells from short-wavelength (blue) cones. Possible mechanisms of the opponent inputs to these bipolar cells are discussed.

Bipolar-amacrine synaptic transmission: Effect of polarization of bipolar cells on amacrine cells in the carp retina*

INTRODUCTION The amacrine cells in the teleost retina are often classified as sustained or transient (1.2). Sustained amacrine cells respond to light with sustained depolarization (ON type) or hyperpolarization (OFF type), while transient amacrine cells respond to both onset and offset of light with a transient depolarization (ON-OFF type). Synaptic transmission from bipolar cells to amacrine cells has been studied by measuring membrane resistance changes accompanying light responses (3), and by examining the effect of chemicals on bipolar and amacrine cell responses (4-7). These studies have suggested that the transmission from bipolar to amacrine cells is excitatory. Furthermore, histological observations on dye-injected bipolar cells and amacrine cells have shown that ON and OFF amacrine cells make synaptic connections with bipolar cells at different sublayers of the inner plexiform layer (8). Thus it is widely believed that ON amacrine cells receive excitatory inputs from depolarizing (ON) bipolar cells, OFF amacrine cells from hyperpolarizing (OFF) bipolar cells, and ON-OFF amacrine cells from both ON and OFF bipolar cells. The above inferences are rather indirect, however, and these observations do not elucidate the kinetics of synaptic transmission between bipolar and amacrine cells. For instance, it remains puzzling how the transient nature of ON-OFF responses is produced by summation of the excitatory inputs from the same ON and OFF bipolar cells that drive the sustained amacrine cells. In this study we approached this problem more directly. We simultaneously recorded responses of a bipolar cell and an amacrine cell with intracellular microelectrodes, while polarizing the bipolar cell with current. A step of depolarizing current injected into ON bipolar cells elicited a steady depolarization in sustained ON amacrine cells, but produced only a transient depolarization at the onset of current in ON-OFF amacrine cells. Steady hyperpolarization of OFF bipolar cells, however, elicited a transient depolarization in ON-OFF amacrine cells at the termination

Methylmercury inhibits gap junctional intercellular communication in primary cultures of rat proximal tubular cells

Abstract Methylmercury (MeHg) causes renal injury in addition to central and peripheral neuropathy. To clarify the mechanism of nephrotoxicity by MeHg, we investigated the effect of this compound on intercellular communication through gap junction channels in primary cultures of rat renal proximal tubular cells. Twenty minutes after exposure to 30 μM MeHg, gap junctional intercellular communication (GJIC), which was assessed by dye coupling, was markedly inhibited before appearance of cytotoxicity. When the medium containing MeHg was exchanged with MeHg-free medium, dye coupling recovered abruptly. However, the dye-coupling was abolished again 30 min after replacement with control medium, and the cells were damaged. Intracellular calcium concentration, [Ca2+]i, which modulates the function of gap junctions, significantly increased following exposure of the cells to 30 μM MeHg and returned to control level following replacement with MeHg-free medium. These results suggest that the inhibiting effect of MeHg on GJIC is related to the change in [Ca2+]i, and may be involved in the pathogenesis of renal dysfunction.

Push-pull modulation of ganglion cell responses of carp retina by amacrine cells

The responses of a ganglion and an amacrine cell were recorded simultaneously in the carp retina. Sinusoidal current injected into amacrine cells modulated ganglion cell discharges either in phase (excitation) or in opposite phase (inhibition). ON-center ganglion cells received excitatory inputs and OFF-center ganglion cells received inhibitory inputs from ON-center amacrine cells. They received inputs of opposite polarity from OFF-center amacrine cells. Namely, inputs from ON-center and OFF-center amacrine cells augment the responses of ON-center and OFF-center ganglion cells in a push-pull manner.