. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 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 vol
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 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. In Figure 3. which
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