Morphological and electrophysiological properties of dissociated primate retinal cells

Although isolated retinal cell preparations have been used widely to study retinal function in lower vertebrates, dissociated cells from primate retina have not been developed for routine physiological experiments. In this study, we demonstrated the feasibility of obtaining viable and identifiable dissociated cells from the primate retina. In addition, we characterized voltage-dependent membrane currents in each type of primate retinal cell with the whole-cell patch-clamp technique. Multiple types of ionic conductance with distinctive current profiles were recorded in various types of primate retinal neurons. Photoreceptors exhibited an inward I(H) activated by membrane hyperpolarization and an outward current activated at depolarized potentials. Two types of potassium currents (transient potassium current, I(K(A)), and delayed rectifier potassium current, I(K(V))) were recorded from bipolar cells. I(K(A)) dominated the current response in putative midget bipolar cells, and I(K(V)) was mainly associated with putative rod bipolar cells. L-type calcium currents (I(Ca)) were observed in primate bipolar cells with axon terminals, but not in axotomized bipolar cells. Large voltage-dependent sodium currents (I(Na)) were only recorded from ganglion cells. Muller cells exhibited I(K(V)) and large potassium inward rectifier current (I(K(IR))), and occasionally a small I(Na). Neurons with electrophysiological signatures of amacrine cells and horizontal cells were also studied even though their morphological features were lost during cell dissociation. By using both morphological and physiological criteria outlined in this report, it is possible to use the dissociated retinal cell preparation as an in vitro system for physiological, biochemical and pharmacological studies of the primate visual system.