Identification of Inwardly Rectifying Potassium Channels in Bovine Retinal and Choroidal Endothelial Cells

Ion channels were studied using the whole-cell patch clamp technique in bovine retinal and choroidal microvascular endothelial cells (MVEC) cultured under the same conditions. The two types of MVEC expressed inward currents at hyperpolarizing voltage steps and showed small outward currents at depolarizing steps. The extrapolated reversal potentials of the inward currents were near to the potassium equilibrium potential. Cs+ and the K+ channel blocker TEA reduced the amplitudes of the currents indicating the selectivity and permeability for potassium. This was confirmed by changes of outside K+ concentration shifting the I-V curves to the right. RT-PCR studies revealed the presence of mRNA of Kir2.1, an inwardly rectifying K+ channel, in retinal and choroidal MVEC. The profile of the small outward currents is related to the Kv family but not identical with the Kv1.4 subtype.