Membrane currents of retinal bipolar cells in culture

Abstract

1. Retinal bipolar cells were isolated from white bass retinas and maintained in a cell culture preparation. Two morphological types of bipolar cells were observed in cell culture. These were labeled large- and small-bipolar cells based mainly on the size of their somata and primary dendrites. Two types of small-bipolar cells were observed. Isolated bass bipolar cells are very similar to those described in the intact retina. 2. Under current clamp, to depolarizing current injection, small-bipolar cells produced a spike followed by a plateau. Large-bipolar cells showed a slow depolarization to a plateau level. 3. Voltage-gated membrane currents were studied using whole-cell patch-clamp techniques. Channel blocking agents were used to define the ion channels found in the membranes of these cells. 4. The large-bipolar cells were found to possess an A-current, a calcium current, and a calcium-dependent potassium current. 5. Large bipolar cells also possessed an inward rectifier that did not correspond to any previously described. 6. The two types of small-bipolar cells were found to have very similar membrane properties to one another. They lacked a large A-current but possessed a slowly activating, outward rectifying potassium current. Similar to the large-bipolar cells, they showed a calcium current and a calcium-activated potassium current. 7. The inward rectifier of small-bipolar cells was characterized as an H-current. 8. The results suggest that the membrane currents of bipolar cells set a narrow operating range about which the cells function in the intact retina. In addition these currents help shape the responses of bipolar cells to light stimuli but do not confer ON or OFF properties.

Mammalian Retinal Bipolar Cells Express Inwardly Rectifying K+ Currents (IKir) With a Different Distribution Than That of Ih

“…Consistent with previous reports (Connaughton and Maguire 1998; Kaneko and Tachibana 1985;Karschin and Wässle 1990;Lasater 1988), we confirmed the presence of I h in bipolar cells. First, we showed in this study that I h is carried by both K ϩ and Na ϩ .…”

“…One component showed instantaneous or time-independent activation, and the second component showed time-dependent activation. The latter resembles the characteristic of I h (DiFrancesco 1993), which has previously been reported in bipolar cells (Connaughton and Maguire 1998;Kaneko and Tachibana 1985;Karschin and Wässle 1990;Lasater 1988). The expression of these two currents was observed in both isolated bipolar cells and bipolar cells in retinal slice preparations.…”

“…However, expression of I Kir in bipolar cells has not been reported previously, although hyperpolarization-activated currents with properties different from those of I h have been observed in fish bipolar cells (Lasater 1988). In this study, we report that bipolar cells in the mammalian retina express I Kir in addition to I h .…”

“…Retinal bipolar cells, including mammalian RBCs, have previously been reported to express I h , which shows timedependent activation (Connaughton and Maguire 1998; Kaneko and Tachibana 1985;Karschin and Wässle 1990;Lasater 1988). As further evidence for the expression of I Kir and the differential expression of I Kir and I h in bipolar cells, we went on to confirm that the time-dependent current in bipolar cells is I h .…”

“…The expression of I h in bipolar cells has been described in a variety of species (Connaughton and Maguire 1998;Kaneko and Tachibana 1985;Karschin and Wässle 1990;Lasater 1988;Tessier-Lavigne et al 1988). However, expression of I Kir in bipolar cells has not been reported previously, although hyperpolarization-activated currents with properties different from those of I h have been observed in fish bipolar cells (Lasater 1988).…”