Developmental expression of the small-conductance Ca2+-activated potassiumchannel SK2 in the rat retina

Small-conductance Ca2+-activated potassium (SK) channels are present in mos t central neurons, where they mediate the afterhyperpolarizations (AHPs) fo llowing action potentials. SK channels integrate changes in intracellular C a2+ concentration with membrane potential and thus play an important role i n controlling firing pattern and excitability. Here, we characterize the ex pression pattern of the apamin-sensitive SK subunits, SK2 and SK3, in the d eveloping and adult rat retina using in situ hybridization and immunohistoc hemistry. The SK2 subunit showed a distinct and developmentally regulated p attern of expression. It appeared during the first postnatal week and locat ed to retinal ganglion cells and to subpopulations of neurons in the inner nuclear layer. These neurons were identified as horizontal cells and dopami nergic amacrine cells by specific markers. In contrast to SK2, the SK3 subu nit was detected neither in the developing nor in the adult retina. These r esults show cell-specific expression of the SK2 subunit in the retina and s uggest that this channel underlies the apamin-sensitive AHP currents descri bed in retinal ganglion cells.