. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 192 H. QIAN ET Figure 1. Examples of two morphological subtypes of bipolar cells isolated from skate retina. The two subtypes are distinguished by their dendritic pattern. (A) Large-field bipolar cells contain several small den- drites that arborize within the outer plexiform layer, and axons that extend downward to the inner plexiform layer of the retina. (B) Small-field bipolar cells have only one (or two) main dendrites. Under whole-cell voltage clamp recording conditions, the small- and large-field bipolar cells exh
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 192 H. QIAN ET Figure 1. Examples of two morphological subtypes of bipolar cells isolated from skate retina. The two subtypes are distinguished by their dendritic pattern. (A) Large-field bipolar cells contain several small den- drites that arborize within the outer plexiform layer, and axons that extend downward to the inner plexiform layer of the retina. (B) Small-field bipolar cells have only one (or two) main dendrites. Under whole-cell voltage clamp recording conditions, the small- and large-field bipolar cells exhibited different volt- age-activated membrane currents. Figure 2A shows typical current recordings from cells held at -60 mV and stepped to membrane potentials from -120 to +60 mV in 20 mV steps (inset). At voltages positive or negative to the resting potential (-40 mV), small-field cells invariably gave rise to larger membrane currents than those of the large-field, gly- cine-insensitive cells. This is clearly evident in the averaged current-voltage relationships for small- and large-field cells shown in Figure 2B, in which the peak amplitudes are plotted as a function of transmembrane voltage. Note also that, although the I-V curves for both cell types display outward rectification, this is much more apparent in the recordings from small-field bipolar cells: , low-ampli- tude membrane currents were elicited at hyperpolarizing voltages between - 120 and -40 mV, but as the magnitude of the depolarizing voltage steps increased from -20 mV to +60 mV, the outward current responses grew linearly at a rate of pA/mV. Nevertheless, the outward currents elicited from both bipolar cell subtypes exhibit little time- dependence. On the other hand, the inward currents induced in small- and large-field bipolar cells by hyperpolari/ing voltage steps differed both in amplitude and time course. The dif- ferences in amplitude are clearly evident in the I-V relations shown in Figure 2B.
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