Inwardly rectifying K+ currents in isolated human retinal pigment epithelial cells.
OBJECTIVE
K+ channels in the retinal pigment epithelium (RPE) play a number of important roles, including the establishment of membrane potential, the transport of K+ between the subretinal space and choroid, and the generation of the c-wave of the electroretinogram. Previous studies on amphibian RPE demonstrated that these functions are likely served by an inwardly rectifying K+ channel. The aim of this study was to characterize inwardly rectifying K+ channels in cultured and freshly isolated adult human RPE (hRPE) cells.


METHODS
Single cells were dispersed enzymatically from primary cultures of adult hRPE or from fresh adult hRPE-choroid. Ionic currents were recorded using either the perforated-patch or whole-cell configuration of the patch-clamp technique.


RESULTS
In 5 mM external K+, roughly 20% of cultured hRPE cells exhibited a strong inwardly rectifying K+ conductance that passed inward but little outward current. This conductance increased when [K+]o was increased and exhibited a voltage-dependent block by external Na+ at negative potentials. In contrast, all freshly isolated hRPE cells exhibited a mild inwardly rectifying K+ conductance that mediated substantial outward current at physiological voltages. This conductance decreased when [K+]o was increased and showed no voltage-dependent block by external Na+.


CONCLUSIONS
The authors conclude that fresh hRPE cells express a mild inwardly rectifying K+ conductance. The operation of this conductance at physiological voltages makes it a likely candidate for the resting K+ conductances of the apical and basolateral membranes. Cultured hRPE cells express a functionally different channel type that may reflect a change in phenotype.
Hughes
B A
BA
Department of Opthalmology, University of Michigan, Ann Arbor 48105, USA.
Takahira
M
M
D000368:Aged; D000369:Aged, 80 and over; D001464:Barium / Q000378:metabolism; D002469:Cell Separation; D002478:Cells, Cultured; D002586:Cesium / Q000378:metabolism; D004553:Electric Conductivity; D005260:Female; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008875:Middle Aged; D018408:Patch-Clamp Techniques; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000502:physiology*; D012964:Sodium / Q000378:metabolism
D015221:Potassium Channels; D002586:Cesium; D001464:Barium; D012964:Sodium; D011188:Potassium