Purpose:
Retinal horizontal cells are second order neurons that modify photoreceptor signals through a feedback circuit. They bear receptors for dopamine. Dopamine release is triggered by light stimulation The aim of this study is to assess the effects of dopamine on the inward rectifier current of cultured retinal horizontal cells.
Methods:
Retinal cell cultures have been prepared from 8-12 day old rabbit and mouse retinae. Cultured rabbit A-type horizontal cells (HC) can be easily detected by their characteristic shape. In cell cultures of mouse retinae identification of putative HC based on their shape and their characteristic Ca 2+- currents has been supported by calbindin staining after recording but has still to be regarded as equivocal since similar criteria apply to at least one type of amacrine cell. Dopamine effects on voltage gated currents were investigated by whole cell patch clamp recording of cells that had been kept in culture for 3 to 14 days.
Results:
Both, rabbit and putative mouse HC show a potassium inward rectifier current (IKir) that can be blocked by Cesium. Adding 1 -10µM dopamine to the extracellular solution increased IKir (155%, average of 11 mouse HC; 141%, average of 18 rabbit HC; 10µM dopamine). Adding GTPßS to the pipette solution inhibited the effect of dopamine. Enhancement by dopamine could be blocked by a 1-10fold concentration of the D1-type antagonist SCH23390 or by an equal concentration of the D2-type antagonist sulpiride. Dopamine effects could be mimicked by a 0.1 fold concentration of the D2 agonist quinpirole but never by the D1 agonist SKF38393.
Conclusions:
Dopaminergic enhancement of the potassium current IKir might serve to steepen the slope of HC light responses and enable them to follow high frequencies of light stimulation.
Keywords: horizontal cells • dopamine • electrophysiology: non-clinical